REDOX TITRATIONS Introduction

REDOX TITRATIONSIntroduction

The complete applications package

At Radiometer Analytical, we put applications first. When you order one of our new genera-tion of titration workstations with a dedicated application package, you have everything youneed to get started right away: electrodes, specific accessories, standards, maintenancesolutions and, of course, methods and application notes.

Application booklets

Redox titrations are frequently used in many industriesand involve potentiometric titrations with or without im-posed current. Instructions for performing some of themost commonly used applications are given in thisbooklet together with calibration procedures for the cor-responding titrants and electrodes. Certain modifica-tions may be needed to take into account specificregulations or standards in force in certain countries, inparticular regarding results presentation.

Radiometer Analytical produces other technique-based applications booklets as well as arange of applications dedicated to particular sectors. Ask your local representative for thefollowing booklets:

Technique Part No.

Acid-base titrations D41T009Precipitation titrations D41T010Complexometric titrations D41T011

Dedicated Part No.

Food and beverage analysis D41T004Plating bath analysis D41T005Water and environmental analysis D41T006Chemical industries D41T007

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TTEP01.09MIN ...................... Operational Qualification (End Point Titration Manager)

TTIP01.01MIN ....................... Operational Qualification (Inflection Point Titration Manager)

TTEP01.03MIN ...................... Calibration of a Ferrous Solution

TTEP01.04MIN ...................... Calibration of an Iodine Solution

TTEP01.08MIN ...................... Calibration of a Thiosulphate Solution

TTEP01.03ENV ..................... Chemical Oxygen Demand of Water

TTEP01.02PLA...................... Analysis of a Chromic Passivation Bath

TTEP01.07AFD ..................... Free Sulphur Dioxide in Wine

TTEP01.06MIN ...................... ClO- Determination in Bleach - Direct Titration with NaAsO2

TTEP01.07MIN ...................... ClO- Determination in Bleach - Indirect Titration

TTIP01.02PET ....................... Bromine Number

TTEP-IP02.01AFD................. Vitamin C in Iodometry

TTIP02.03PLA ....................... Cu in Electroless Copper Baths Redox

TTIP02.01AFD....................... Peroxide Number of Edible Oils

TTIP02.01MIN ....................... Hydrogen Peroxide Determination

TTEP-IP02.01ENV ................ Dissolved Oxygen in Water

TTEP-IP02.02AFD................. Iodine Value of Animal and Vegetable Fats and Oils

REDOX TITRATIONS

D41

T01

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End Point Titration ManagerOperational Qualification

Introduction

The operational qualification pro-cedure demonstrates that an in-strument runs according to theoperational specifications in theselected environment. For an endpoint titration manager, this opera-tion can consist of two steps:- Calibration and checking of a pHmeasurement electrode system- Titration of anhydrous sodiumcarbonate standard using a com-mercial standard solution of HCl.

Principle

The reaction has 2 steps

Na2CO

3 + HCl � NaHCO

3 + NaCl

NaHCO3 + HCl � CO2 + H2O + NaCl

corresponding to 2 different endpoints.The operational qualification takesinto account the second equiva-lence point (pH 3.90) correspond-ing to the complete neutralisationof sodium carbonate.

Electrode and reagents

pHC2011-8 Combined pH Elec-trode (part no. E16M317)

T201 Temperature Sensor (partno. E51M001)

IUPAC Series pH standardspH 4.005 (part no. S11M002),pH 7.000 (part no. S11M004) andpH 10.012 (part no. S11M007)

100 g bottle of Merck "certified"sodium carbonate (part no.1.06394.0100) or 500 g bottle of"pro analysis" Merck sodium car-bonate (part no. 1.06392.0500)

1 l of "ready to use" Merck HCl0.1 mol/l (part no. 1.09060.1000)

Distilled water

End Point titration settings

ElectrodepH: pHC2011-8Calibration request: YESNumber of cycles: 2Number of buffers: 3Measurement: StirringTemperature: probe

Calibration parametersStability: 15 mpH/minAcceptation time: 2.00 minMax. stab. Time: 5.00 minAcceptation criteria: YESIso. pH: 6.65 pH

Calibration solutions1: 4.005 (IUPAC)2: 7.000 (IUPAC)3: 10.012 (IUPAC)Min. zero pH: 5.8 pHMax. zero pH: 7.5 pHMin. sensitivity: 95%Max. sensitivity: 103%

TitrantID: HClUnit: MTitre: Entered

MethodPredose: see belowStart timer: 45 secMax. volume: see belowNumber of EP: 1Min. speed: 0.2 ml/minMax. speed: 5.00 ml/minDirection: decreasing pHEnd point: 3.90 pHDelay: 10 secProportional band: 3.00 pH

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ResultsSample unit: mgNumber of result: 1Acceptation criteria: YESResult unit: %Molar weight: 105.99Reaction: 1 smp + 2 titrMinimum value: 99Maximum value: 101

Procedure

Electrode calibration andcheckingIf the electrode is new, condition itby immersion in distilled water forat least 1 hour

Connect the pHC2011-8 combinedpH electrode and the T201 Tem-perature Sensor

Using the above-mentioned set-tings, RUN an electrode calibra-tion with 2 or more cycles

At the end of the last cycle, cali-bration results should be accepted

Ensure that the temperature of thestandards does not differ by morethan 2°C.

End point titration operationqualificationFit the titration manager with HCl0.1 M as titrant and install thetitrant.

Preparation of Na2CO3As indicated, dry approximately 5 gof anhydrous sodium carbonate inan oven for 4 hours at 250°C. Letit cool to room temperature in adesiccator with P2O5

or anotherhumidity adsorber.

End point titrationTo determine the necessaryamount of sodium carbonate

With a 25 ml burette capacityWeigh exactly 85-90 mg ofNa

2CO

3

This weight corresponds to1.6-1.8 meq or 16-18 ml of HCl0.1M. Use a predose correspond-ing to 10 ml and a maximum vol-ume of 25 ml

With a 10 ml burette capacityUse the same settings as the25 ml burette capacity

With a 5 ml burette capacityWeigh exactly 40-45 mg ofNa

2CO

3

Use a maximum volume of 10 ml

No predose.

Dissolve the weighed sodium car-bonate quantitatively in the titra-tion beaker with 50 to 80 ml offreshly distilled water.

Immerse the electrode and thedelivery tip in the solution.

Using the above-mentioned set-tings, run a titration with 3 differentsamples. Results should be ac-cepted between 99 and 101%.

End Point Titration Manager Operational Qualification

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Inflection Point Titration ManagerOperational Qualification

Introduction

The operational qualification pro-cedure demonstrates that an in-strument runs according to theoperational specifications in theselected environment. For a titra-tion manager using automaticinflection point determination, thisoperation can consist of two steps:

- Calibration and checking of a pHmeasurement electrode system,

- Titration of anhydrous sodiumcarbonate standard using a com-mercial standard solution of HCl.

Principle

The reaction has 2 steps corre-sponding to 2 different inflectionpoints:

Na2CO

3 + HCl � NaHCO

3 + NaCl

NaHCO3 + HCl � CO

2 + H

2O + NaCl

The operational qualification takesinto account the second equiva-lence point (close to pH 4.00)

corresponding to the completeneutralisation of sodium carbonate.

The Titration Manager settingsallow the complete titration curveto be seen.


pHC2011-8 Combined pH Elec-trode (part no. E16M317)

T201 Temperature Sensor (partno. E51M001)

IUPAC Series pH standards

pH 4.005 (part no. S11M002)

pH 7.000 (part no. S11M004)

pH 10.012 (part no. S11M007)

100 g bottle of Merck "certified"sodium carbonate (part no.1.06394.0100) or 500 g bottle of"pro analysis" Merck sodium car-bonate (part no. 1.06392.0500)

1 l of "ready to use" Merck HCl0.1 mol/l (part no. 1.09060.1000)

Distilled water

Continuous IP titrationsettings

ElectrodepH: pHC2011-8Calibration request: YESNumber of cycles: 2Number of buffers: 3Measurement: StirringTemperature: probe

Calibration parametersStability: 15 mpH/minAcceptation time: 2.00 minMax. stab. Time: 5.00 minAcceptation criteria: YESIso. pH: 6.65 pH

Calibration solutions1: 4.005 (IUPAC)2: 7.000 (IUPAC)3: 10.012 (IUPAC)Min. zero pH: 5.8 pHMax. zero pH: 7.5 pHMin. sensitivity: 95%Max. sensitivity: 103%

TitrantID: HClUnit: MTitre: Entered

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MethodStirring speed: 550 rpm

Predose: 0 mlStart timer: 45 secMax. volume: (see notes)Stop point: 2.000 pHSmoothing parameter: 8Number of IP: 2Min. speed: 0.2 ml/minMax. speed: 5.00 ml/minDirection: decreasing pH

Inflection 1Min. ordinate: 7.00 pHMax. ordinate: 10.00 pHInflection 2Min. ordinate: 2.80 pHMax. ordinate: 6.00 pH

Sample unit: mgSample amount: (see notes)

ResultsResults by: cumulateNumber of result: 1Acceptation criteria: YES

Result 1Result unit: %Molar weight: 105.99Reaction: 1 smp + 2 titrCalculate with IP: 2Minimum value: 99Maximum value: 101

Procedure

Electrode calibration andcheckingIf the electrode is new, condition itby immersion in distilled water forat least 1 hour.Connect the pHC2011-8 electrodeand the T201 Temperature SensorUsing the above-mentioned set-tings, RUN an electrode calibra-tion with 2 or more cycles.At the end of the last cycle, cali-bration results should be acceptedEnsure that the temperature of thestandards does not differ by morethan 2°C.

Operation qualification in con-tinuous IPFit the burette of the titration man-ager with HCl 0.1 M as titrant andinstall the titrant

Preparation of Na2CO3As indicated, dry approximately5 g of anhydrous sodium carbon-ate in an oven for 4 hours at250°C. Let it cool to room tem-perature in a desiccator with P2O5or another humidity adsorber.

Notes

To determine the necessaryamount of sodium carbonate

With a 25 ml burette capacity

Weigh exactly approximately85-90 mg of Na

2CO

3

This weight corresponds to

1.6-1.8 meq or 16-18 ml of HCl0.1M. Use a maximum volumeclose to 20/22 ml

With a 10 ml burette capacity

Weigh exactly approximately 40 mgof Na

2CO

3. Use a maximum vol-

ume of 10 ml

With a 5 ml burette capacityWeigh exactly approximately 20 mgof Na

2CO

3. Use a maximum vol-

ume of 5 ml

Dissolve the weighed sodium car-bonate quantitatively in the titra-tion beaker with 50 to 80 ml offreshly distilled water.

Immerse the electrode and thedelivery tip in the solution.

Using the above-mentioned set-tings, run a titration on 3 differenttests or replicates. Results shouldbe accepted between 99 and 101%.

Inflection Point Titration Manager Operational Qualification

Calculations are programmed togive a result according to the de-livered titrant volume at the inflec-tion point situated in the accept-ance range 2.80-6.00 pH

Dynamic IP Titrationsettings

This application note can be usedwith incremental addition of titrant(Dynamic IP)

Dynamic IPSpeed: 5.00 ml/minDynamic dose: 30Maximum dose: 0.3 mlStability: 100 mpH/minAcceptation: 10 s

These settings were tested with a10 ml burette. The others settingsare unchanged.

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Calibration ofa Ferrous Solution Fe(II)

Reagent preparation

The most common Fe(II) salt isMohr's salt: (NH

4)2Fe(SO

4)

2, 6H

20

(molecular weight 392.14 g/mol)To prepare a 0.1 eq/l 1000 ml so-lution, proceed as follows:Weigh 39.21 g of Mohr's salt anddissolve in 500 ml of distilled wa-terAdd 100 ml of sulphuric acid ap-proximately 1NUsing a volumetric flask,dilute to1000 ml with distilled water

Standard preparation

One of the most common standardsin redox analysis is potassiumdichromate K

2Cr

2O

7 (molecular

weight 294.19 g/mol).Potassium dichromate solutionsare very stable.The oxidation power of potassiumdichromate is based on the reac-tion

Cr2O7- - + 14H+ + 6 e- � 2Cr+++ + 7H2O

A 0.1 eq/l potassium dichromatesolution contains 1/60 mole ofdichromate.To prepare 1000 ml of 0.1 eq/lK2Cr2O7 proceed as follows:

Dry the potassium dichromate(analytical grade) for 2 hours at120°C and leave it to cool at roomtemperature in a desiccator.

Weigh exactly 4.90317 (294.19/60) gand dissolve with freshly distilledwater to exactly 1000 ml using avolumetric flask.


MC3051Pt-9 Metal Electrode, plati-num combined (part no. E31M003)with CL114 cable (part no. A94L114)

50% H2SO

4 in water

Dilute the same volume of con-centrated sulphuric acid in a givenvolume of distilled water. As theoperation is very exothermic, makethis dilution very slowly accordingto laboratory safety regulations.

Freshly distilled water

K2Cr

2O

7 0.1 eq/l standard solution


Burette volume: 25 mlStirring speed: 400 rpmWorking mode: mV with i = 0Number of end points: 1End point: 690 mVStirring delay: 30 secondsMinimum speed: 0.1 ml/minMaximum speed: 5.0 ml/minProportional band: 350 mVEnd point delay: 5 secondsDirection: Decreasing mVSample unit: mlStandard amount: 20Standard conc.: 0.1 eq/lResult: eq/l

Procedure

Prepare the titration system with a25 ml burette and 0.1 eq/l ferroussolution as titrant.

Connect the MC3051Pt-9 elec-trode to input E1 via cable CL114.

Pipette exactly 20 ml of K2Cr

2O

70.1 eq/l standard.

Add 10 ml of 50% H2SO

4 solution

and complete to 100 ml with dis-tilled water.

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Start method by pressing the RUNkey.

Results

The result is expressed as eq/lconcentration and based on thefollowing formula

Vol(FeII salt) * C(FeII salt) =Vol(K

2Cr

2O

7) * C(K

2Cr

2O

7)

The calibration result can beaccepted if 5 determinationsgive a result with a relativestandard deviation of less than0.5%.

Notes

a) Using a solution as standard, itis best to use a standard concen-tration close to the titrant concen-tration. This allows closed vol-umes for titrant and standard.For the best result accuracy, pi-pette a standard volume corre-sponding to a delivered titrantvolume greater than 50% of theused burette cylinder.

b) The application note uses a25 ml cylinder capacity. If you usea 5 or 10 ml cylinder for the bu-rette, pipette 5 ml of standard andmodify the method as follows:

Predose: 2 mlMaximum volume: 8 ml

c) It is possible to calibrate theferrous titrant by weighing anamount of potassium dichromate.

With a 25 ml burette cylinder ca-pacity

Exactly weigh approximately 95 mgof potassium dichromate

In the STANDARD screen ENTER

Standard unit: mgStandard amount: xx.xConcentration unit: %Concentration: 100

(or purity of the standard)Molecular weight: 294.19

And in the RESULT screen ENTER

Result: eq/lCoefficients: 1 Standard + 6 Titrant

Note that for FeSO4, concentration

in eq/l is the same as in mol/l.

Calibration of a Ferrous Solution Fe(II)

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Calibration of an Iodine Solution

Reagent preparation

To prepare 0.1 eq/l iodine solutionwhich can be used in a very widepH range, we can dissolve iodine(I

2) in a solution of potassium io-

dide. Iodine in redox reaction re-acts according to

I2 + 2e- � 2I-

A 0.1 eq/l iodine solution con-tains 0.05 mol/l or1/20 mol/l of iodine

I2 has a molecular weight corre-

sponding to 235.8 g/mol

To prepare a 0.1 eq/l iodine solu-tion, dissolve 40 g of potassiumiodide in 50 ml of distilled waterthen add 12.69 g (235.8/20) ofanalytical grade iodine, wait for itto dissolve completely and com-plete to 1.000 ml with a volumetricflask.

Store the solution in a brown glassbottle.


To calibrate iodine solution, useAs

2O

3 as standard. It has a mo-

lecular weight of 169.87.

The redox reaction between iodineand As(III) is

1(As2O3) + 2(I2) + 5H2O à 4I- + 2AsO4--- + 10H+

A 0.1 eq/l As III solution contains1/40 As

2O

3 mol/l.

To prepare the 0.1eq/l As IIIstandard solution.

Weigh 4.2467 (169.87/40) g ofpure As

2O

3 and dissolve it in

about 20 ml of NaOH 10M. Youcan gently heat the solution todissolve it faster.

Add about 200 ml of pure waterand H

2SO

4 1M until the pH

reaches 8.00.

Leave the solution to reach roomtemperature.

Complete to exactly 1000 ml witha volumetric flask.


For this reaction, the best titrationprocedure is a pre-set end pointtitration using imposed currentpotentiometry with a double plati-num wire electrode.

The curve shape is very sharparound the equivalent point.

M231Pt2 Metal Electrode, doubleplatinum wire (part no. E32M001)with adapter part no. A94P801(BNC/2xbanana) or M241Pt2-8with BNC plug (part no. E32M002)

Distilled water

Na2CO

3 saturated solution in wa-

ter or pH 10.00 buffer solution(part no. S11M014)


Burette volume: 25 mlStirring speed: 400 rpmWorking mode: mV with i > 0Imposed current: 5µA AC or DCNumber of end points: 1End point: 50 mVStirring delay: 60 secondsMinimum speed: 0.1 ml/min

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Maximum speed: 6.0 ml/minProportional band: 500 mVEnd point delay: 10 secondsDirection: Decreasing mVSample unit: mlStandard amount: 20Standard conc.: 0.1 eq/lResult: eq/l

Procedure

Prepare the titration system with a25 ml burette and 0.1 eq/l iodineas titrant.

Connect the M231Pt2 electrodevia the adapter part no. A94P801.

In a beaker, pipette 60 ml of pH10.00 buffer solution or the samequantity of saturated Na

2CO

3 solu-

tion.

Pipette exactly 20 ml of As2O

30.1 eq/l standard.


Results

The result is expressed as eq/lconcentration and based on thefollowing formula:

Vol(As2O

3) * C(As

2O

3) = Vol(I

2) * C(I

2)

The calibration result can beaccepted if 5 determinationsgive a result with a relativestandard deviation of less than0.5%.

Notes

a) Using a solution as standard, itis best to use a standard concen-tration close to the titrant concen-tration. This allows closed vol-umes for titrant and standard.

For the best result accuracy, pi-pette a standard volume corre-sponding to a delivered titrantvolume greater than 50% of theused burette cylinder.

b) The application note uses a25 ml cylinder capacity. If you usea 5 or 10 ml cylinder for the bu-rette, pipette 5 ml of standard andmodify the method as follows:


c) If you calibrate an iodine solu-tion using DC or AC imposed cur-rent you must use this titrant usingthe same imposed current proce-dure.

Calibration of an Iodine Solution

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Calibration of aThiosulphate Solution


To prepare a 0.1 eq/l (or 0.1 mol/)sodium thiosulphate solution, dis-solve 24.8181 g of Na

2S

2O

3, 5H

2O

in 500 ml of freshly distilled water(or freshly boiled and cooleddeionised water) and 2 or 3 dropsof CHCl

3 (or also 0.4 g of NaOH)

and complete to 1000 ml using avolumetric flask.

Wait for one day and filter the so-lution if necessary (precipitation ofsulphur can occur).Stock the solution in a brownglass flask.

Look at the solution from time totime and filter again if necessary.

Solutions with a concentrationbelow 0.01N (or 0.01M) are notstable.

Na2S

2O

3, 5H

2O has a molecular

weight corresponding to248.181 g/mol.


To calibrate a thiosulphate solution,use potassium iodate KIO

3 as

standard. It reacts with potassiumiodide KI giving iodine I

2 according

to the reaction

IO3- + 5I- + 6H+ � 3I

2 + 3H

2O

The thiosulphate ion reacts with I2

according to the reaction

3I2 + 6S

2O

3-- � 6I- + 3S

4O

6--

The molecular weight of KIO3 is

214.0 g/mol. A 0.1 eq/l iodatesolution, according to the above-mentioned reactions (1 ion IO

3-

corresponds to 3I2), contains

1/60 mol/l of KIO3.

Weigh exactly 3.5667 g of potas-sium iodate (214/60) and dilute in1000 ml of distilled water using avolumetric flask.


For this reaction, the best titrationprocedure is a pre-set end pointtitration using imposed currentpotentiometry with a double plati-num wire electrode.

The curve shape is very sharparound the equivalence point.

M231Pt2 Metal Electrode, doubleplatinum wire (part no. E32M001)with adapter part no. A94P801(BNC - 2xbanana) or M241Pt2-8Metal Electrode, double platinumwire with BNC plug (part no.E32M002).

Distilled water

KI, solid state

HCl, concentrated


Burette volume: 25 mlStirring speed: 400 rpmWorking mode: mV (with i>0)Imposed current:10 µA (AC or DC)

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Predose: 15 ml (see note)Number of end points: 1End point: 200 mVStirring delay: 60 secondsMinimum speed: 0.1 ml/minMaximum speed: 2.5 ml/minProportional band: 200 mVEnd point delay: 5 secondsSample unit: mlStandard amount: 20Standard conc.: 0.1 eq/lResult: eq/lTitration: Increasing mV

Procedure

Prepare the titration system with a25 ml burette and 0.1 eq/l sodiumthiosulphate as titrant.

Connect the M231Pt2 electrodevia the adapter or the M241Pt2-8electrode directly.

Pipette 20 ml of the KIO3 standard

solution, add 30 ml of distilledwater, about 1 g of solid KI. Waitfor dissolution, then slowly add5 ml of concentrated HCl.

Dip electrode and delivery tip inthe solution.


Results

The result is expressed as eq/lconcentration and based on thefollowing formula:

Vol(S2O3--) * C(S2O3

--) = Vol(IO3-) * C(IO

3-)

With C(IO3

-) expressed in eq/l

The calibration result can beaccepted if 5 determinationsgive a result with a relativestandard deviation below 0.5%.

Notes

1) The titration curve shows acharacteristic shape with a veryflat first part and a sharp secondpart. To save time, it is thereforeadvisable to use a predose and anot too high burette speed toavoid "over-titrating".

2) The application note uses a25 ml cylinder capacity. If you usea 10 ml cylinder for the burette,pipette 5 ml of standard, with a5 ml burette pipette, also 5 ml ofstandard and modify the methodas follows:


3) Instead of an aqueous solutionof KIO

3, you can use solid state

KIO3. In this case and for the ap-

plication note conditions, exactlyweigh approximately 60 mg ofKIO

3 (for 20 ml of sodium thiosul-

phate solution) and in theSTANDARD screen ENTER

Standard unit: mgStandard amount: xx.xConcentration unit: %Concentration: 100

(or purity of the standard)Molecular weight: 214

And in the RESULT screen ENTER

Result: eq/lCoefficients: 1 standard and 6 titrants

Calibration of a Thiosulphate Solution

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Chemical Oxygen Demandof Water

Introduction

Chemical Oxygen Demand (COD)is an important parameter forwastewater or surface water test-ing and plants.This determination gives informa-tion about the degree of waterpollution by organic material.This application note concernsCOD determination by potassiumdichromate. Another method usingpotassium permanganate is usedfor low COD determinations.

Principle

Organic matter contained in awater sample is oxidised in 50%sulphuric acid, by a known excessof potassium dichromate. Afterdigestion, remaining unreduceddichromate is determined by po-tentiometric titration using a Fe(II)solution according to the followingreaction:

Cr2O72- + 2Fe++ + 14H+ � 2Cr+++ + 6Fe+++ + 7H2O

A blank titration with distilled wateras sample is run for every cycle.

The result is expressed as oxygenequivalent.


For titration in a beaker

M231Pt Metal Electrode, platinum(part no. E31M002) with CL114cable (part no. A94L114)

REF601 Reference Electrode,mercurous sulphate (part no.E21M012)

For titration directly in digestionflask

MC602Pt Metal Electrode, com-bined platinum/mercurous sulphate(part no. 945-360)

Titrant (NH4)2Fe(SO

4)

2, 6H

20

(Mohr's salt) 0.15 eq/l (MW =392.14 g/mol)

Weigh and dissolve 58.82 g ofMohr's salt in 500 ml of distilledwater

Add 100 ml of sulphuric acid ap-proximately 1N

Using a volumetric flask, dilute to1000 ml with distilled water

Calibrate as indicated in separateapplication note

Potassium dichromate 0.25 eq/lsolution or 0.0417M (K

2Cr

2O

7)

(A 0.1 eq/l K2Cr

2O

7 solution con-

tains 1/60 mole of K2Cr

2O

7 that has

a molecular weight of 294.19 g/mol)

Dry the potassium dichromate(analytical grade) for 2 hours at120°C and let it cool to room tem-perature

Weigh exactly 12.258 g and dis-solve exactly with freshly distilledwater to 1000 ml using a volumet-ric flask

Sulphuric acid reagent

Add 5.5 g of Ag2SO

4 to 1 kg of

concentrated H2SO

4 and leave to

stand for 2 days to dissolve theAg

2SO

4

Solid mercuric sulphate HgSO4


Back titration with blankBurette volume: 25 mlStirring speed: 400 rpmWorking mode: mV (with i=0)Back titration: ManualNumber of end points: 1End point: 300 mVStirring delay: 30 seconds

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Minimum speed: 0.1 ml/minMaximum speed: 2.5 ml/minProportional band: 350 mVEnd point delay: 5 secondsSample unit: mlSample amount: 20Blank volume:

determined by blank titrationExcess: 0.0 mlTitration: Decreasing potential

ResultsResults number: 1Result unit: mg/l

Procedure

Blank preparation and titration

Using distilled water as sample,prepare and titrate a blank with thesame procedure and reagents (seebelow)

Accept the obtained titrant volumeas blank volume

The theoretical blank volume canbe calculated according to thefollowing formula:

Vol. of blank = 10 * 0.25 / 0.15 =16.67 ml

10 = volume of K2Cr

2O

7 solution in

ml

0.25 = Concentration of K2Cr2O7 ineq/l

0.15 = concentration of Mohr's saltsolution in eq/l

Sample preparation

Place 20 ml of water in a 250 mlrefluxing flask or in a special CODtube. Add 0.4 g of HgSO

4 and

glass beads and very slowly 2 mlof sulphuric reagent while mixing.Then add 10.00 ml of dichromatesolution and 28 ml of sulphuricacid reagent and connect to con-denser. Mix thoroughly and boilunder reflux during 2 hours.

After rinsing condenser with5/10 ml of distilled water, transferto titration beaker using 25/30 mlof distilled water to rinse. Totalvolume does not exceed 100 ml.

Sample titration

Prepare the titration manager with25 ml burette and 0.15 eq/l ferroussolution as titrant.

Connect M231Pt electrode via theCL114 cable and the REF601 refer-ence electrode or, if necessary, theMC602Pt combined electrode.

Dip electrodes and delivery tip inthe sample beaker.

Start method by pressing the RUN key.

Results

Expressed as mg/l of oxygenequivalent according to

COD (in mg/l of oxygen) = (Vbl - Vtit)* C * 8 * 1000 / Vsample

Vbl = titrant volume consumedduring blank titration (close to16.67 ml for application note con-ditions)

Vtit = titrant volume consumedduring sample titration

(Vbl - Vtit) = directly calculated byTIM8xx

C = titrant concentration in mol/l orequivalent/l

8 = equivalent weight for oxygen(16/2)

Vsample = sample volume in ml

For a result in mg/l of oxygen

Enter

The sample amount in the SAMPLEscreen

The titrant concentration in theTITRANT screen

1 Titrant and 1 Sample in theCOEFFICIENTS display

8 as equivalent weight for oxygen

The Titration Manager gives aresult according to the above for-mula, as (Vbl - Vtit) is directlycalculated by the Titration Manager.

Chemical Oxygen Demand in Water

For 5 determinationsMean: 450 mg/l oxygenStandard deviation: 15 mg/lRel. standard deviation: 3%

Working range

With application note conditions,titrant concentration of 0.15 eq/land sample volume of 20 ml

(Vbl - Vtit) = 1 ml corresponds toa COD of 60 mg/l

(Vbl - Vtit) = 15 ml corresponds toa COD of 900 mg/l

Notes

The Titration Manager uses thesame electrodes for titration andreagent calibration. For titrant cali-bration with the electrodes in thisnote, you can use the applicationnote TTEP01.03MIN with a changein the end point potential.

The latest standard NF T 90.101(2001)uses the same procedure but usesas reagents

(NH4)2Fe(SO4)2, 6H20 (Mohr's salt)0.12 mol/lPotassium dichromate solution or0.040 mol/l (K2Cr2O7)

And works with 10 ml of sample

Bibliography

EPA method number 410.1Standard methods for water andwastewater 18th edition (1992) 5-6part 5220ISO 6060 (1989)NF T90-101 (2001)

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Analysis of a ChromicPassivation Bath

Introduction

In the car industry, the analysis ofa chromic passivation bath con-sists of a determination of theconcentration of dichromate ion byredox titration with ferrous sul-phate as titration reagent.The result is expressed as "points",i.e. the number of millilitres of0.1 eq/l titrant used for a givenamount of sample, generally 50 or100 ml.

Principle

The titration reaction occurs ac-cording to the following reaction

6Fe++ + Cr2O72- + 14H+ � 6Fe+++ + 2Cr+++ + 7H2O

This reaction takes place in strongacidic media.


MC3051Pt-9 Metal Electrode,combined, platinum (part no.E31M003) with CL114 cable (partno. A94L114)

Ferrous sulphate solution 0.1 eq/l

Weigh and dissolve 39.21 g of(NH

4)

2Fe(SO

4)

2, 6H

20 (Mohr's salt)

in 500 ml of distilled water.Add 100 ml of sulphuric acid ap-proximately 1N.Using a volumetric flask, dilute to1000 ml with distilled water.

50% H2SO

4 in water

Dilute the same volume of con-centrated sulphuric acid in a givenvolume of distilled water. As thisoperation is very exothermic, runthe dilution very slowly accordingto laboratory safety regulations.


Burette volume: 25 mlStirring speed: 400 rpmWorking mode: mVNumber of end points: 1End point: 690 mVStirring delay: 30 secondsMinimum speed: 0.1 ml/minMaximum speed: 2.5 ml/minProportional band: 250 mVEnd point delay: 5 seconds

Sample unit: mlSample amount: 100Result: mlTitration: Decreasing mV

Procedure

Prepare the Titration Managerwith a 25 ml burette and 0.1 eq/lferrous solution as titrant.

Connect the electrode to the inputby means of the CL114 cable.

Pipette the required amount ofsample (generally 100 ml).

Add 25 ml of 50% H2SO

4 solution

for 100 ml of sample.



Results

Expressed as ml of 0.1 eq/ltitrant for 100 ml of sample

R = V(titr)

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If the titrant used is not exactly0.1 eq/l in concentration and if thesample amount is not 100 ml,correct as follows:

R = V(titr) * 100 * C(titr) / V(smp) * 0.1

-V(titr) = total volume of titrant toreach the end point in ml

-V(smp) = current sample amount

-C(titr) = exact concentration ofthe titrant

5 determination results inpoints or ml of titrantMean: 8.50 mlStandard deviation: 0.076 mlRel. standard deviation: 0.9%

Working range

As the result for a 100 ml samplevolume and a 0.1 eq/l titrant isdirectly the delivered volume oftitrant, the working range for thebest possible accuracy and repro-ducibility is between 8.75 and 25ml for the application note condi-tions.

Notes

1) Remember that strong acidicmedia are necessary for this re-dox titration (see the reaction for-mula)

2) 50% sulphuric acid can be re-placed by 50% phosphoric acid

3) The 30-second stirring delay isnecessary to allow the platinumelectrode to reach a stable poten-tial

4) If the titrant used is not 0.1 eq/l,you need to multiply the resultobtained by a factor, F determinedas follows:

F= current titre (expressed ineq/l)/ 0.1

Analysis of a Chromic Passivation Bath

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Free Sulphur Dioxide in Wine(Modified Ripper method)

Introduction

Sulphur dioxide is present inwines as free SO

2 and also bound

to acetaldehyde. The sum gives"total" sulphur dioxide. Bound SO

2is released by addition of NaOH1M to the wine sample.

This application is dedicated tofree SO

2 measurement.

As a rule, determination of SO2 in

wines by the modified Rippermethod uses a coloured indicatorto determine the equivalencepoint, but it is also possible to usea pre-set end point titration withimposed current potentiometry.

With this end point method, manychemical functions present in thewine can modify the electrodebehaviour and the reaction kinetics.

This application note gives amodified procedure suitable formany wines (white, red or rosé).We have tested various differentwines but not all those availableworldwide. This method has notbeen tested on special types ofwine such as sparkling or sweetwines.

Principle

SO2 is determined by titration with

iodine solution according to thereaction

HSO3

- + I2 + H

2O � SO

4-- + 2I- + 3H+

Free SO2 is measured directly in

acidic media.

The titration is run according to apre-set end point titration withimposed current potentiometryand a double platinum wire elec-trode.

Results are expressed as SO2 in

mg/l.


M231Pt2 Metal Electrode, doubleplatinum wire (part no. E32M001)with adapter part no. A94P801 orM241Pt2-8 Metal Electrode with-out adapter (part no. E32M002)

Iodine solution 0.01 mol/l (0.02 eq/l)

25% v/v H2SO4 solution in distilledwater

Dilute 250 ml of concentrated sul-phuric acid in 750 ml of distilled

water. This operation is highlyexothermic so perform the dilutionvery slowly and respect laboratorysafety regulations. Let the solutioncool down to room temperature.This solution is approximately 9Nor 4.5M.

Kl 5%

Dilute 50 g of potassium iodide in1000 ml of distilled water.

NaHCO3 solid form (see notes

and remarks)


Burette volume: 10 mlStirring speed: 400 rpmWorking mode: mV with i = 1 µA

(DC)Number of end points: 1End point: 100 mVStirring delay: 10 secondsMinimum speed: 0.2 ml/minMaximum speed: 5.0 ml/minProportional band: 500 mVEnd point delay: 5 secondsSample unit: mlSample amount: 50 ml for free SO

2Titration: Decreasing potentialResult: mg/l

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Procedure

Free SO2Pipette 5 ml of H

2SO

4 solution

25% v/v into a low diameterbeaker, add 10 ml of KI solution5% and 50 ml of wine, and titratequickly with 0.01M Iodine solu-tion. Addition of NaHCO

3 indicated

in some local procedures can beavoided if titration occurs quickly.

Results

Expressed as mg/l of SO2 (MWof 64 g/mol)

Using as titrant unit: mol/l (M)In this case, as 1 mole of titrantreacts with 1 mole of SO

2 (or

HSO3-) in the sample:

R = V(titr) * C(titr) * 64 * 1000 / V(smp)

-V(titr) = Total volume of titrant toreach the end point (in ml)

-C(titr) = Concentration of titrant inmol/l

64 = Molecular weight of SO2 in

g/mol

-V(smp) = sample volume in ml

For a result in mg/l with theTitration ManagerEnter

The actual sample amount in theSAMPLE screen

The titrant concentration in theTITRANT screen (in mol/l)


64 as molecular weight

The Titration Manager gives aresult according to the above for-mula.

Using as titrant unit eq/l and 64for molecular weight of SO2Note that in this case, 2 eq.titrants (I

2 corresponds to 2I) react

with 1 sample.

For a result in mg/lEnter

The actual sample amount in theSAMPLE screen

The titrant concentration in theTITRANT screen (in eq/l)

2 Titrants and 1 Sample in theCOEFFICIENTS display

64 as molecular weight

The Titration Manager gives aresult according to the above for-mula.

Statistics

For 5 determinations with awhite wineFree SO2Mean: 35 mg/l SO

2Standard deviation: 0.7 mg/l SO

2Rel. standard deviation: 2%

Procedure forred and rosé wines

With red wines, a secondary slowreactions between the iodine andtannin and other products canoccur. Although addition of KI isnot always necessary with whitewines, it is compulsory for redand rosé wines. Addition of KI(potassium iodide) eliminates orreduces secondary slow reactionsbetween iodine and reducingproducts present in red wine

Titrate immediately using thetitration settings above

Free Sulphur Dioxide in Wine (Modified Ripper method)

Results for free SO2 in red orrosé wines

(4 tests on each kind of wine)Grenache (red wine)Mean: 23.1 mg/lStand dev.: 0.7 mg/lResult (1): 21.7 mg/l

Merlot (red wine)Mean: 15.2 mg/lStand dev.: 0.5 mg/lResult (1): 16.0 mg/l

Syrah (red wine)Mean: 16.9 mg/lStand dev.: 0.4 mg/lResult (1): 15.6 mg/l

(Results verified free SO2 determi-

nation measured by aspirationmethod)(1) (Result for aspiration method)

Rosé wine(3 determinations)Mean: 20.3 mg/lStand dev.: 0.2 mg/l

Verification of the free SO2 con-tent by addition of Na2SO3aqueous solution before titration(The solution S1 contains 12.0 g/lof Na

2SO

3 or 6.2 mg/ml of SO

2)

50 ml Rosé wine 20.3 mg/l50 ml Rosé wine + 0.2 ml of S1

42.0 mg/lTheoretical 20 + 24 = 44 mg/l

50 ml of red wine 1 24.4 mg/l50 ml of red wine 1 + 1 ml S1

126 mg/lTheoretical 24.4 + 120 = 144 mg/l

50 ml of red wine 2 29.7 mg/l50 ml of red wine 2 + 0.1 ml of S1

41 mg/lTheoretical 29.7 + 12 = 42 mg/l

50 ml of red wine 2 + 0.2 ml of S151 mg/l

Theoretical 29.7 + 24 = 54 mg/l

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Note that the recovery of addedSO

2 is not 100% because the

wine immediately binds part ofthis "SO

2".

Working range

For free SO2 determination, using

a 0.01 mol/l titrant and 50 ml forsample volume, 1 ml of titrantcorresponds to 12.8 mg/l SO

2

Automation of the free SO2 de-termination

Using a sample changer (SAC8015 position), it is not recom-mended to add H

2SO

4 and KI for

too long before the titration. TheKI/H

2SO

4 mixture is not stable as

in these conditions I- is oxidisedgiving I2.

Add the KI solution manually tothe different beakers and use aperistaltic pump for H

2SO

4 addi-

tion.

Tests were run using a Watson-Marlow Alitea 400 (040.1501.D1E)peristaltic pump fitted with siliconetubing (ext. diameter 7 mm int.diameter 4 mm). With this tubingand a speed setting of 6, it takes12 seconds to deliver 10 ml (typi-cal value).

Fit the silicone tubing in the headof the pump.

Dip one end of the tubing in theH

2SO

4 solution bottle and fit the

other with a glass delivery tip forexample.

Set the pump (potentiometer in 6position and in CW or clockwise )

Connect the pump to the mainsand let it run until the air bubblesin the tubing are eliminated

Disconnect the pump.

Connect the pump to the 5 V TTLoutput

Black plug of the Titration Man-ager to pin 8 of the external com-mand plug

Red plug of the Titration Managerto pin 4 of the external commandplug

Set the pump

Potentiometer in position 6 and inCW (clockwise) position

Connect the pump to the mains

The pump does not start as it iscontrolled by the titration man-ager.

Titration Manager settings

Use the above settingsJust add method parameters

Auxiliary output: 5 VAux. On for: 12 seconds

Note that use of twin headperistaltic pump allows simultane-ous automatic addition of the twosolutions at (H

2SO

4 25% and KI

5%) the beginning of the titration.

Notes

This method, named Ripper'smethod, is less accurate than theaspiration method because part ofthe iodine can be consumed byreducing substances other thanSO

2.

Using the aspiration method, SO2

is removed from the sample by astream of air through the acidifiedsample and oxidised in H

2SO

4.

Then H2SO

4 is titrated by NaOH.

In some cases, the modified Rip-per method can give higher re-sults than expected with winescontaining a significant amount ofascorbic acid because this acid(and some others) reacts quanti-tatively with iodine.

Adding NaHCO3 forms a CO

2blanket over the sample, whichprevents oxygen interference dur-ing the titration. Addition should beavoided if the titration is runquickly in a covered beaker.

As it is easy to lose SO2 during

the preparation of the sample,make sure you titrate the sampleimmediately after preparation.

Imposed current values of 1 µAand 5 µA (DC) were tested with-out change in the results.

Titrant concentrations correspond-ing to 0.01M and 0.05M were alsotested without change in the titra-tion speed reaction and in theresults.

Bibliography

Techniques for chemical analysisand quality monitoring during winemakingPublished by Patrick ILAND winespromotion CampbelltownAUSTRALIA

Free Sulphur Dioxide in Wine (Modified Ripper method)

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ClO- Determination in BleachDirect Titration with NaAsO2

Introduction

A bleach solution contains mainlyNaClO plus basic products suchas NaOH and Na

2CO

3.

ClO- can be determined directlyby redox titration. The titrationresult is generally expressed as a% of ClO-.

Principle

Direct titration of ClO- by NaAsO2

uses the following redox reaction

AsO2- + ClO- + 2OH- � AsO4

--- + Cl- + H2O

Note that in this reaction, whichinvolves 1 mole ClO- for 1 moleAsO

2-, 2 oxidation numbers are

exchanged (As (III) to As (V) andCl(1) to Cl(-1).This reaction needs a pH ofaround pH 10.00The titration is run according to apotentiometric pre-set end pointtitration using a combined plati-num/reference electrode.


MC3051Pt-9 Metal Electrode,combined platinum (part no.E31M003) with CL114 cable (partno. A94L114)

Distilled water

pH 10.00 Buffer Solution (part no.S11M014)

NaAsO2 0.1 eq/l solution in water

To prepare the 0.1 eq/l (or 0.05 mol/l)NaAsO

2 solution

As a 0.1 eq/l NaAsO2 solution

contains 1/40 As2O

3 mol/l

Weigh 4.2467 (169.87/40) g ofpure As

2O

3 and dissolve it in

about 20 ml of 10M NaOH. Youcan gently heat the solution tohave a quick dissolution

Add about 200 ml of pure waterand 1M H

2SO

4 until the pH reaches

8.00

Leave the solution to reach roomtemperature

Dilute to 1000 ml exactly with avolumetric flask


Burette volume: 25 mlStirring speed: 400 rpmWorking mode: mVNumber of end points: 1End point: 200 mVStirring delay: 30 secondsMinimum speed: 0.1 ml/minMaximum speed: 10 ml/minProportional band: 375 mVEnd point delay: 5 secondsSample unit: mlSample amount: 0.5Titration: Decreasing potentialResult: g/l

Procedure

Install the titration system with theNaAsO

2 solution

Connect the electrode

Pipette (or preferably weigh) thesample amount

Dilute the sample with 50 ml ofpH 10.00 buffer solution

Dip electrode and delivery tip inthe solution

Start method by pressing the RUNkey

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ClO- Determination in Bleach - Direct Titration with NaAsO2

Results

Commonly expressed as g/l ofClO- (MW = 51.43 g/mol)

Use as titrant unit: mol/l (M)

As 1 mole of titrant reacts with1 mole of ClO- in sample:

R = V(titr) * C(titr) * 51.43 / V(smp)

V(titr) = total volume of titrant toreach the end point (in ml)

C(titr) = concentration of titrant inmol/l

51.43 = molecular weight of ClO-

V(smp) = sample volume in ml

For a result in g/l

Enter




51.43 as molecular weight

The Titration Manager gives aresult according the above for-mula.

Using eq/l as titrant unit

Enter



2 Titrants and 2 Samples in theCOEFFICIENTS display


The Titration Manager gives aresult in g/l according the aboveformula.

For a result as a %

As the Titration Manager cannotgive a result in % if the sampleunit is a volumetric unit, you canuse the equation feature:

Equation number: 1Equation result: % ClOEquation formula:R1 / 10

R1 is the titration result calculatedin g/l

5 determinations on a commer-cial concentrated bleach

Mean (as ClO-): 76.5 g/lStandard deviation: 1.2 g/lRel. standard deviation: 1.6%

Working range

As a commercially available con-centrated bleach corresponds to aClO- concentration in g/l of around80 (corresponding to a total vol-ume of titrant of around 16 ml for0.5 ml of sample), it is possible touse the dilution procedure to facili-tate pipetting or weighing 0.5 ml ofsample.

For example, pipette 5 ml of sam-ple, dilute to 100 ml with waterand take an aliquot of 10 ml.

In the SAMPLE display enter

DILUTION: YESSample: 5 mlFinal dilution volume: 100 mlAliquot: 10 ml

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ClO- Determination in BleachIndirect Titration

Introduction

A bleach solution contains mainlyNaClO plus basic products suchas NaOH and Na

2CO

3.

ClO- can be determined by redoxtitration. Besides the direct titrationby sodium arsenite; ClO- determi-nation can be run with a two-steptitration; quantitative oxidation of I-

by ClO- giving I2 and titration of I

2by sodium thiosulphate. The titra-tion result is generally expressedas % of ClO-.

Principle

Oxidation of I- by ClO- follows thereaction

ClO- + 2I- + H2O � I

2 + Cl- + 2OH-

Titration of I2 by sodium thiosul-

phate follows the reaction

I2 + 2 S

2O

32- � S

4O

62- + 2I-

The result of these 2 equations is1 ion ClO- corresponds to 2 ionsS

2O

32-

The titration of I2 by S

2O

32- is run

by pre-set end point titration withimposed current potentiometry.


MC231Pt2 Metal Electrode, dou-ble platinum wire, with adapterpart no. A94P801 (BNC/2xbanana)or M241Pt2-8 Metal Electrode

Distilled water

KI solid state

HCl pure grade

Na2S

2O

3 0.1 eq/l or 0.1 mol/l (For

concentration determination seeseparate application note)

Weigh exactly 24.8181 g ofNa

2S

2O

3, 5H

2O

Dissolve in 500 ml of freshlyboiled distilled water

Add 2 or 3 drops of CHCl3Dilute to 1000 ml in a volumetricflask

Wait for one day and filter if nec-essary

Store in a brown glass bottle


Burette volume: 25 mlStirring speed: 400 rpmWorking mode: mV with i = 10 µA (DC)Number of end points: 1End point: 200 mVStirring delay: 40 secondsMinimum speed: 0.1 ml/minMaximum speed: 5.0 ml/minProportional band: 200 mVEnd point delay: 5 secondsSample unit: mlSample amount: 0.5Titration: Increasing potentialResult: g/l

Procedure

Install the titration system with theNa

2S

2O

3 solution

Connect the electrode

Pipette (or preferably weigh) thesample amount

Dilute the sample with 50 ml ofdistilled water

Add 1 g of KI and 5 ml of HCl

Dip electrode and delivery tip inthe solution

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ClO- Determination in Bleach - Indirect Titration

Start method by pressing the RUNkey

Results

Commonly expressed as g/l ofClO- (MW = 51.43 g/mol)

Use as titrant unit: mol/l (M)

As 2 moles of titrant correspondsto 1 mole of ClO- in sample:

R = V(titr) * C(titr) * 51.43 / 2 * V(smp)

V(titr) = total volume of titrant toreach the end point (in ml)

C(titr) = concentration of titrant inmol/l

51.43 = molecular weight of ClO-

V(smp) = sample volume in ml

For a result in g/l

Enter



2 Titrants and 1 Sample in theCOEFFICIENTS display


The Titration Manager gives a re-sult according the above formula.

For a result as a %

As the Titration Manager cannotgive a result in % if the sampleunit is a volumetric unit, you canuse the equation feature

Equation number: 1Equation result: % ClOEquation formula:R1 / 10

R1 is the titration result calculatedin g/l

5 determinations on a commer-cial concentrated bleach

Mean (as ClO-): 78.8 g/lStandard deviation: 1.2 g/lRel. standard deviation: 1.6 %

Working range

As a commercially available con-centrated bleach corresponds to aClO- concentration in of around80 g/l (corresponding to a totalvolume of titrant of around 16 mlfor 0.5 ml of sample), it is possibleto use the dilution procedure tofacilitate pipetting or weighing 0.5ml of sample.

For example, pipette 5 ml of sam-ple, dilute to 100 ml with waterand take an aliquot of 10 ml.

In the SAMPLE display enter

DILUTION: YESSample: 5 mlFinal dilution volume: 100 mlAliquot: 10 ml

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Bromine Number of Petroleum Products(ASTM D1159-98 Electrometric titration)

Introduction

This method covers bromine numberdetermination of certain petroleumproducts indicated in ASTM stand-ard D1159-98. The magnitude ofthe bromine number is simply anindication of the bromine reactiveconstituents, not an indication ofthe constituents.The bromine number mainly indi-cates the concentration of doublebonds present in the product.

Principle

Expressed as g of Bromine (Br2)

able to react with 100 g of product,the bromine number determinationuses the reaction between a (Br-/BrO

3

-) solution and the petroleumproduct according to the followingreactions

a) 5 Br- + BrO3

- + 6H+ 3Br

2 + 3H

2O

b) Br2 + R-C=C-R R-C-C-R

| | Br-Br

(main reaction with product)

(Note that other reactions canoccur such as addition, substitu-tion or oxidation)

To avoid secondary reactionsthe titration is run at low tem-perature (close to 5°C).The titrant concentration, ex-pressed as Br

2 concentration, is

0.25 mol/l (or ¼ mol/l). According toreaction (a), the titrant contains5/12 mole of KBr and 1/12 mol/l ofKBrO

3.The molar weight of KBr is

119.9 g/mol and for KBrO3 167.9 g/mol.

Titration is run according to aninflection determination with im-posed current potentiometry and adouble platinum wire electrode.


M241Pt2-8 Metal Electrode, dou-ble platinum (part no. E32M002)orM231Pt2 Metal Electrode, doubleplatinum (part no. E32M001) withadapter part no. A94P801

T201 Temperature sensor (partno. E51M001)

Water-jacketed titration beakerconnected to a low temperaturethermostat or a bath filled with ice

Bromide-Bromate titrant solution(0.25 mol/l as bromine concentration)

Dissolve 51.0 g of KBr (5*119.9/12)and 13.92 g of KBrO

3 (167.01/12)

in 1000 ml of distilled water usinga volumetric flask.

Sulphuric acid (1+5)

Carefully mix one volume of con-centrated sulphuric acid with 5volumes of distilled water. Caution:the dilution reaction is exothermic.

Titration solvent (see notes)

Mix 714 ml of glacial acetic acid(CH

3COOH), 134 ml of dichloro-

methane (CH2Cl

2), 134 ml of

methanol (CH3OH) and 18 ml of

sulphuric acid (1+5).

Dichloromethane (CH2Cl

2)

Warning: Reagents used in thisapplication note are flammable.They can cause severe burns andare hazardous if swallowed, breathedor come into contact with the skinor eyes. Always respect laboratoryhealth and safety regulations whenusing these reagents.

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Inflection Detectionsettings

CONTINUOUS IPTitration with blankBurette volume: 10 ml (see notes)Max. volume: 7 mlStirring speed: 500 rpmWorking mode: mV with i >0Current: DCCurrent value: 5µA (see notes)Blank: YESStart timer: 30 sStop point: 0 mV

Minimum speed: 0.50 ml/minMaximum speed: 2.00 ml/minSmoothing param: 8

Titration: Decreasing potentialInflection number: 1Stop at last IP: YES

Inflection 1:Min. ordinate: 200 mVMax. ordinate: 800 mV

Sample

Dilution: YESSample unit: gSample amount: 2

(see working range)Final dilution vol.: 50 mlAliquot: 5 ml

(see working range)

Result 1: ml

Equation 1:Equation Unit: Bromine numberEquation: (R1*CT*15.98*DA/(SA*AL)

(see notes)

Procedure

Connect the double platinum wireelectrode to the corresponding in-put of the Titration Manager.

Connect the temperature sensor tothe corresponding input on theTitration Manager.

For a new titration solvent batchrun a BLANK titration with 115 mlof titration solvent and 5 ml ofdichloromethane. The experimentalblank volume is generally lowerthan 0.1 ml.

Sample preparationPlace 10 ml of dichloromethane ina 50 ml volumetric flask then addthe weighed sample and fill theflask to the mark withdichloromethane.

Add 110 ml of titration solvent tothe titration beaker.

Add an aliquot (generally 5 ml butnot more than 10 ml) of the samplesolution in dichloromethane.

Dip the electrode, temperature sen-sor and delivery tip in the beakerand immerse the beaker in an icebath or alternatively in a low tem-perature thermostatic bath.

Using the electrode direct measure-ment function of the TitrationManager (icon ELECTRODES and"DISPLAY MEASUREMENT) allowthe solution to reach the mentionedtemperature (around 5°C) (seenotes).

Run the titration.

Bromine Number of Petroleum Products (ASTM D1159-98 Electrometric titration)

Results

As indicated above, results areexpressed in g of Br2 able toreact with 100 g of product.

R(bromine number) =(Vtitr - Vblk) * C(titr) * 159.8 * 100/ W(smp) * 1000

Vtitr = Total volume of titrant usedin mlVblk = Blank volume used forsolvent titrationC (titr) = Concentration of titrant inmol/lW (smp) = Sample weight in g159.8 = molecular weight of Br

2

100 = conversion factor for 100 gof product1000 = correction factor for resultin g instead of mg

For 5 determinations oncyclohexene (C6H10)Mean delivered volume: 3.42 mlRel. standard deviation: 1.2%Corresp. Bromine number: 193Theoretical: 194.6

Working range

For a sample amount of 1g, and acalculated dilution coefficient of 10(50 ml for final dilution volume and5 ml for the aliquot), 1 ml of 0.25 mol/ltitrant corresponds to a Brominenumber of 37.5.

The magnitude of the bromine numberof a sample is often unknown andit is necessary to perform a pre-liminary test with 2 g of sample.

ASTM Standard D1159 gives atable for sample amount as a func-tion of Bromine number:

Bromine number Sample amount in g Titrant volume in ml 0-10 20-16 Around 410-20 10-8 Around 3-420-50 5-4 Around 5

50-100 2-1.5 Around 4100-150 1.6-0.8 Around 3-4150-200 0.8-0.6 Around 3-4

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Notes

Notes regarding the titrationsolventASTM Standard D1159 givestrichloroethane as an alternativefor dichloromethane. However, theuse of this solvent is forbidden inmany countries.To save time, you can store thetitration solvent in a refrigeratorbetween the experiments.

Note regarding the maximumvolumeTo avoid a two-phase system dur-ing titration, it is not recommendedto use a titrant volume higher than10 ml.

Note regarding the imposedcurrentA 1 µA imposed current can givenoisy curves and 10 µA gives acurve that is not well definedaround the inflection point.Instead of DC imposed current it ispossible to use AC imposed cur-rent. A 25 µA AC imposed currentgives titration curves similar tothose obtained with 5 µA DC current.In this case, also modify the "Br-Nb-Ctrl-Temp" method.

Note regarding the equationThe entered equation takes intoaccount the programmed dilutionof the sample.DA is the final dilution volume andAL the aliquot volume.

Note regarding sample handlingFor sample and dichloromethanehandling, you can use a glasssyringe instead of a pipette.

Note regarding temperaturemeasurementAs indicated previously, you canuse the DISPLAY MEASUREMENTfunction, but in this case you canjust check the temperature of thesolution (DISPLAY MEASUREMENTchecks the measured potential onE1 and E2 inputs, not on Pt-Ptinput). You can use this informationin the pre-programmed method"Br- Nb-Ctrl-Temp" that measuresthe potential of the double platinumwire electrode AND the sampletemperature.

Note regarding the curve shapeBased on experience, the startingpotential may be around 1300 mVand suddenly falls to around 800 mVat the beginning of the titration.Then the curve falls very quicklyto the final measured potential(generally around 100 mV) nearthe inflection point.

Bromine Number of Petroleum Products (ASTM D1159-98 Electrometric titration)

Curve

mV

ml0.8 1.6

1000

700

400

3.22.4

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Iodometric Titration of Vitamin C(pre-set end point and inflection detection methods)

Introduction

Vitamin C (ascorbic acid or itssodium salt) is naturally present infresh fruit juices or vegetables. Itis also used in some pharmaceuti-cal products. The food industrymakes use of vitamin C as ananti-oxidation additive in cookedpork meats or canned products toavoid oxygen action (E300 forascorbic acid or E301 for the so-dium salt according to Europeanregulations).

Summary

Many redox titrations can be usedfor Vitamin C determination.In some cases, depending on themedia, iodometric back titration ispossible, for example in freshlemon juice or preservatives forfood products.

Vitamin C formula

The redox titration is a two-stepreaction.First stepOxidation of Vitamin C with excessiodine (I

2).

The redox reaction involves thetwo –OH groups according to:

HO-C=C-OH + I2 O=C-C=O +2I- +2H+

Second stepThe iodine excess is then deter-mined by sodium thiosulphateaccording to:

I2 + 2S

2O

32- 2I- + S

4O

62-

As results are generally expressedin mg/l, % or mg/kg, note that themolar weight of the Vitamin C is176.3 g/mol corresponding to theglobal formula C

6H

8O

6. The molar

weight of sodium ascorbate(C

6H

7O

6Na) is 198.3 g/mol.


Electrode for pre-set end pointtitrationM241Pt2-8 Metal electrode, dou-ble platinum (part no. E32M002)orM231Pt2 Metal electrode, doubleplatinum (part no. E32M001) withadapter part no. A94P801

Electrode for inflection detec-tionMC3051Pt-9 Metal electrode com-bined, platinum (part no. E31M003)with CL114 cable (part no. A94L114)

Reagents0.05 mol/l iodine solution:Dissolve 40 g of potassium iodidein 50 ml of distilled water then add12.69 g of analytical grade iodine,wait for complete dissolution andcomplete to 1.000 ml with a volu-metric flask.Store the solution in a brown glassbottle.

HO OH

C

CC

OCH CHOH

OCH2OH

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0.1 mol/l thiosulphate solution:Dissolve 24.8181 g of Na

2S

2O

3,

5H2O in 500 ml of freshly distilled

water (or freshly boiled andcooled deionised water) and 2 or3 drops of CHCl

3 (or 0.4 g of

NaOH) and complete to 1000 mlusing a volumetric flask.Wait for one day and filter the so-lution if necessary (precipitation ofsulphur can occur).Stock the solution in a brown glassflask.

These two solutions are commer-cially available.

Sodium acetate buffer solutionDissolve 85 g of sodium acetate(CH

3COONa) in water, add 60 ml

of glacial acetic acid and dilute to1000 ml with freshly distilled wa-ter. This solution contains approxi-mately 1 mole of CH

3COOH and

1 mole of CH3COONa per litre.

Freshly distilled water.

End Point Titration settings

Burette volume: 25 ml(for iodine solution)

Burette volume: 10 ml(for thiosulphate solution)

Stirring speed: 400 rpm

Working mode: mV i>0Current: DCCurrent value: 5 µAStart timer: 10 secondsMaximum volume: 10 mlDirection: Increasing mVMinimum speed: 0.2 ml/minMaximum speed: 2.00 ml/min

Back Titration: Automatic(see Back titration note)

Excess reagent: I2 0.05MExcess volume: 15 ml

Number of end points: 1End point: 200 mVProportional band: 190 mVEnd point delay: 5 seconds

Sample unit: g or mlSample amount: Depending onthe product (see below)

Result: %Molar weight: 198 g/molExcess: 2Smp + 2ExcReaction: 1Exc + 2Titr

(see Result note)

Inflection Detection settingsContinuous IP mode

Burette volume: 25 ml(for iodine solution)

Burette volume: 10 ml(for thiosulphate solution)


Working mode: mVStart timer: 10 secondsMaximum volume: 10 mlStop point: 150 mVDirection: decreasing mVMinimum speed: 0.2 ml/minMaximum speed: 4.00 ml/minSmoothing parameter: 5

Back Titration:Automatic (see Back titration note)Excess reagent: I

2 0.05M

Excess volume: 15 ml

Inflection No 1Minimum ordinate: 230 mVMaximum ordinate: 350 mVSample unit: g or mlSample amount: Depending on theproduct (see below)

Result: %Molar weight: 198 g/molExcess: 2Smp + 2ExcReaction: 1Exc + 2Titr

(see note Result)

Iodometric Titration of Vitamin C (pre-set end point and inflection detection methods)

Procedure

Using a biburette Titration Man-ager, fill burette 1 with thiosul-phate solution and burette 2 withiodine solution.

With a monoburette Titration Man-ager, fill the burette with thiosul-phate solution, and add the iodinesolution manually.

Connect the electrode.

Add 10 ml of sodium acetate buffersolution and, if necessary, freshlydistilled water to the sample.

Dip electrode and delivery tip inthe solution and run the titration.

Results

The general formula for resultexpression is:

Csmp

= 1/Ksmp

* (Cexc

* Vexc

- (Ctitr * V

titr/2))

- 1/Ksmp

is a function of the sampleamount and unit- C

exc concentration of the iodine

solution in mol/l- V

exc added volume of iodine solu-

tion in ml- C

titr concentration of titrant solu-

tion in mol/l (thiosulphate solution)- V

titr used volume of thiosulphate

solution in ml

Using the above-mentioned coeffi-cients for excess and reaction, theTitration Manager takes into ac-count this formula for result calcu-lation.

For 3 determinations with afood preservativeThis is a mixture of sodium chlo-ride, sodium acetate and vitamin C

Mean: 6.55%

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Working range

Using an iodine solution with aconcentration of 0.05 mol/l,1 ml of the iodine solution reactswith 0.05 mmole corresponding to8.81 mg of Vitamin C.Take this into account to deter-mine the approximate amount ofiodine solution necessary for thereaction and add an excess corre-sponding to approximately 50% ofthis volume.

For low concentrations, it is possi-ble to use 0.005mol/l iodine solu-tion and 0.01mol/l thiosulphatesolution.

Notes

Back titrationSet "AUTOMATIC" using a bi-burette Titration Manager. With amonoburette system, set "MANUAL"and enter excess reagent concen-tration and volume. Other settingsare unchanged.

ResultNote that, in back titration, theTitration Manager asks for theSAME COEFFICIENTS for sampleand titrant. It is therefore compul-sory to set the titration system asindicated.

Iodometric Titration of Vitamin C (pre-set end point and inflection detection methods)

mV

ml3 5

600

400

200

874 6

mV

ml3 5

330

250

874 6 9

Continuous IP mode

End point titration

Curves

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Copper in Electroplating Copper Baths(Redox Titration Method)

Introduction

Electroless copper baths, used inparticular in the manufacture ofprinted circuits, contain coppersalts, sodium hydroxide stabilisingagents and formol, but many elec-troplating copper baths containacids (H2SO4) or cyanide ion.

For these baths, copper determi-nation can involve a redox titrationinstead of E.D.T.A.

Principle

The redox titration of copper ioninvolves a two-step reaction:

First step: oxidation of iodide ion I-by Cu2+ with iodine formation

2Cu2+ + 4I- 2CuI + I2

Second step: titration of generatedI2 with thiosulphate ion

I2 + 2S2O32- S4O6

2- + 2I-

Regarding the 2 reactions, 1 moleof Cu2+ corresponds to 1 mole ofS2O3

2-

The titration uses a combinedplatinum/reference electrode.


MC3051Pt combined platinum/reference electrode (partno. E31M003)

CL114 connecting cable (partno. A94L114)

Potassium iodide solution

Dissolve 80 g of potassium iodidein 1000 ml of distilled water.

Glacial acetic acid

Sodium thiosulphate solution0.1 mol/ (or 0.1N)

Na2S2O3, 5H2O has a molecularweight corresponding to248.181 g/mol

To prepare a 0.1 equivalent/l (or0.1 mol/) sodium thiosulphatesolution; dissolve 24.8181 g ofNa2S2O3, 5H2O in 500 ml offreshly distilled water (or freshlyboiled and cooled desionised

water) and 2 or 3 drops of CHCl3and complete to 1000 ml using avolumetric flask

Wait for one day and filter the so-lution if necessary (precipitation ofsulphur can occur)

Stock the solution in a brownglass flask

Look at the solution from time totime and filter and standardiseagain if necessary

This solution is also commerciallyavailable.

Distilled water.

Inflection DetectionSettings

CONTINUOUS IP MODE

Burette volume: 10 ml(see working range)


Working mode: mVStart timer: 5 minMaximum volume: 10 ml

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Stop point: 170 mVDirection: decreasing mVMinimum speed: 0.1 ml/minMaximum speed: 5.00 ml/minSmoothing parameter: 5

Minimum ordinate: 200 mVMaximum ordinate: 320 mVStop at last IP: YES

Sample unit: mlSample amount: (see working range)Dilution: NO (see working range)

Result: g/lMolar weight: 159 g/molReaction: 2Smp + 2Titr

Procedure

For a sulphuric acid/Copper bath

For an expected concentration ofCuSO4 close to 75 g/l, pipette 1 mlof sample, add 10 ml of distilledwater and 15 ml of CH3COOHand complete to 60 ml with dis-tilled water.

Stir the solution and add 5 ml ofKI solution.

The solution becomes dark yellowand cuprous iodide precipitates.

Run the titration.

The start timer set to 5 minutesallows a complete reduction ofCu2+.

At the end of the titration, the solu-tion may be colourless with awhite precipitate of cuprous io-dide.

The complete sample preparationand titration procedure changeaccording to the sample composi-tion.

As a general rule, the copper re-duction (first step reaction) andthe iodine reduction (titration) takeplace in acidic media (pH 2.00/4.00).

Copper in Electroplating Copper Baths (Redox Titration Method)

Results

As indicated, 1 mole of Cu2+ cor-responds to 1 mole of S2O3

2-

R(g/l) = Vtitr * Ctitr * 159.58 / Vsmp

Vtitr = Total volume of titrant usedin mlCtitr = Concentration of titrant inmol/lVsmp = Sample volume in ml159.58 = Molar weight of CuSO4in g/mol

3 determinations on the samebath

Mean: 74.20 g/lStandard deviation: 0.2 g/l

Working range

The table below can be used as aguideline according to the copperconcentration:

This table takes into account theabove-mentioned concentrationsfor reagents and titrant.

Instead of 1 ml for sample amount,it is possible to take 10 ml of sam-ple diluted to 100 ml with a volu-metric flask and use 10 ml of thediluted solution.In this case, modify the TitrationManager settings as follows:

Sample unit: mlDilution: YESSample amount: 10Final dilution amount: 100Aliquot: 10

Notes

Procedure:Addition of KSCN (potassium thio-cyanate) avoids adsorption of I2on CuI and improves accuracy ofthe method.Depending on the bath composi-tion, it can be necessary tochange the sample preparation.If the solution contains cyanideion, add 3 ml of sulphuric acid and1 ml of nitric acid to 1 ml of sam-

ple under a hood, gentlyboil until white fumes arereleased then add waterand ammonium hydroxideto pH 6.00 and then glacialacetic acid.

To obtain a well-shapedtitration curve as shown inthe graph and a correct

result, make sure sufficient glacialacetic acid is added.

Curve

mV

ml

1 3

330

270

762 4 5

CuSO4 conc. g/l 10 80 160

Sample ml 10 1 1

Burette capacity ml 10 10 25

KI added 5 5 10

Titrant used 6.25 5 10

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Peroxide Number of Edible Oils(NF T 60-220 (1995) and ISO 3960 (2001))

Introduction

The peroxide number is a meas-urement of the concentration of(-O-O-) groups in edible oils. It is ameasurement of the decomposi-tion of the product and in manycountries, official standards specifya maximum peroxide numberbeyond which the oil is unfit forhuman consumption. The peroxidenumber is therefore measured byoil manufacturers during produc-tion and after storage to check itspreservation.International standards use a redoxtitration in non-aqueous media,results are generally expressed inµg of peroxide (or active oxygen)per gram of product but mmoles/kgor meq of O2/kg are also used.The following two standards usethe same titration principle but notthe same solvents.NF T 60-220 uses chloroform CHCl3ISO 3960 uses isooctane C8H18

According these two standards,the equivalence point of theredox titration is determinedusing starch as colour indica-tor, but it is very easy to usepotentiometric determination.

Summary

Peroxide number determinationinvolves a two-step redox reaction:

1) Reaction of peroxide group withan excess of iodide ion according to:

R-O-O-R + 2I- + 2H+ 2ROH + I2

2) Titration of Iodine with Na2S2O3solution (generally 0.01 or 0.02M)according to:

I2 + 2S2O32- 2I- + S4O6

2-

The titration is run according toinflection detection with continu-ous addition of the titrant with acombined platinum/referenceelectrode.


MC3051Pt-9 Metal electrode,combined, platinum (part no.E31M003) with CL114 cable (partno. A94L114).

Glacial acetic acid (CH3COOH)Chloroform (CHCl3) (NF T 60-220)Isooctane C8H18 (ISO 3960)

Solvent used for ISO 3960

Acetic acid/isooctane solution bymixing of 3 volumes of glacialacetic acid and 2 volumes ofisooctane.

Saturated aqueous solution ofpotassium iodide (KI)

Note that the solubility of KI inwater is approximately 150g/100 mlof water.

Do not prepare too a large volumeof this solution. Store it in the dark.

Distilled water

Sodium thiosulphate solution0.01M (or 0.02 mol/l) in water(Na2S2O3)

To prepare a 0.01 mol/l (or 0.02 mol/l)sodium thiosulphate solution, dis-solve 2.4818 g (or 4.9636 g) ofNa2S2O3, 5H2O in 500 ml offreshly distilled water (or freshlyboiled and cooled deionised wa-ter). Add 2 or 3 drops of CHCl3 (or0.4 g of NaOH), as stabilisingagent, and complete to 1000 mlusing a volumetric flask.

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Wait for one day and filter the so-lution if necessary (precipitation ofsulphur can occur).

Stock the solution in a brownglass flask.

From time to time, look at the so-lution and filter or standardiseagain if necessary.

Na2S2O3, 5H2O has a molecularweight corresponding to248.181 g/mol.

As solutions with a concentrationcorresponding to 0.01M are notvery stable, do not store this solu-tion for more than 1 week.

As Sodium thiosulphate solution0.1M is commercially available,you can prepare the 0.01 or 0.02Msolution by dilution.

Check that solvents and reagentsdo not contain dissolved oxygen.

Bubbling nitrogen in the differentsolutions is one way to do this.

Inflection Detectionsettings

CONTINUOUS IP MODE

Titration with blankBurette volume: 5 ml

(see working range)Max. volume: 3.5 mlStirring speed: 500 rpmWorking mode: mV i=0Blank: YESStart timer: 10 sMin. ordinate: 150 mVMax. ordinate: 250 mVStop point: 0 mV

Minimum speed: 0.20 ml/minMaximum speed: 3.00 ml/minSmoothing parameter: 4

Titration: Decreasing potentialInflection number: 1Inflection 1:Min. ordinate: 150 mVMax. ordinate: 280 mVStop at last IP: YES

SampleDilution: NOSample unit: gSample amount: 2

(see working range)

ResultsResult 1:Unit: mg/kgReaction: 1 sample + 2 TitrantMolar weight: 16 g/mol

(see results)

No of equations: 2Equation 1Unit: mmoles O2/kgFormula: R1/16Equation 2Unit: meq O2/kgFormula: R1/8

Procedure

According to NF T 60-220

Use a stoppered titration vessel.

First run a blank titration accord-ing the following procedure butwithout sample.

Then run a titration.

Accurately weigh the necessaryamount of edible oil.

Add 10 ml of chloroform and stirto dissolve.

Add 15 ml of glacial acetic acidand 1 ml of saturated potassiumiodide solution.

Stop the titration vessel, stir for1 minute and wait 5 minutes,keeping away from daylight.

Then add 75 ml of distilled waterand titrate with 0.01 (or 0.02 mol/l)thiosulphate solution.

Peroxide Number of Edible Oils (NF T 60-220 (1995) and ISO 3960 (2001))

Procedure according to ISO 3960

The general procedure is exactlythe same as for NF T 60-220.

Weigh the necessary sampleamount.

Dilute with 50 ml of the isooctane/acetic acid solution.

Add 0.5 ml of potassium iodidesolution and stir for 1minute thenadd 30 ml of distilled water.

Results

Expressed as µg/g (or mg/kg) ofactive oxygen the results corre-sponds to:

R = Ctitr * Vtitr * 16 * 1000 / 2 * Wsmp

Ctitr = Titrant concentration in mol/lVtitr = Necessary titrant volume in ml1000 = Constant to express theresult in µg16 = molar weight of oxygen2 = As 2 moles of titrant corre-spond to 1 mole of sampleWsmp = Weighed amount of sam-ple in g

Some other units can be used forresult expression.

Result in mmoles/kg correspondsto: R/16Result in meq of active oxygen/kgcorresponds to: R/8

Results3 determinations on old peanutoilMean: 192.8 mg/kg

(standard deviation: 2.6)12.05 mmoles O2/kg

(standard deviation: 0.16)24.10 meq O2/kg

(standard deviation: 0.33)(blank determination: 0.107 ml

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Working range

Use the following table whichsummarises the data in bothstandards to determine the neces-sary amount of sample:

Peroxide Number of Edible Oils (NF T 60-220 (1995) and ISO 3960 (2001))

Peroxide number Peroxide number Sample amount Titrant volumeµg/g or mg/kg meq/kg (g) (ml)

0-100 0-12 5.0-2.0 2.4

100-150 12-18.75 2.0-1.2 2.25

150-250 18.75-31.25 1.2-0.8 2.25-1.5

250-400 31.25-50 0.8-0.5 1.5-2.5

400-700 50-87.5 0.5-0.3 2.5-2.6

(*) Calculated with oleic acid molar weight(**) For a 0.1M titrant

Notes

Procedure

The main difficulty is to obtainreproducible results avoiding theinfluence of atmospheric oxygen.

Note that the saturated solution ofpotassium iodide is highlyoxidisible. It is necessary to checkthis solution using the thiosul-phate 0.01M solution according tothe procedure described in thestandards.

Low values for blanks are recom-mended (between 0.05 and 0.1 mlaccording to the standards).

After addition of water, the titrationmedium is a two-phase solution.Check you immerse the measur-ing electrode in the aqueousphase. Do not use too high a titra-tion speed, because it is neces-sary to free all the iodine from thesolvent layer.

mV

ml0.9 1.8

300

260

220

3.62.7

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Hydrogen Peroxide Determination(by manganimetric titration)

Introduction

Discovered in 1818 by a Frenchchemist, L.J Thenard, Hydrogenperoxide (H2O2) is a commonoxidising agent used inpapermaking as well as in thetextile or pharmaceutical industry.It is used for disinfecting and col-our removal.The dismutation reaction of hydro-gen peroxide corresponds to thefollowing equations:

H2O2 + 2H+ + 2e 2H2O

H2O2 O2 + 2H+ + 2e

The global reaction corresponds to:

2H2O2 2 H2O + O2 (1)

Principle

H2O2 determination generallyuses a redox titration using potas-sium permanganate as oxidisingagent according to the followingreaction:

5H2O2 + 2MnO4- + 6H+

5O2 + 2Mn2+ + 8H2O

As indicated, the reaction takesplace in acidic media (generally insulphuric media).The H2O2 titration is run usingpotentiometry with a combinedplatinum/reference electrode.Results are generally expressedas a % of H2O2 or in volumes ofoxygen by volume of solution.The titre as a % indicates theweight of H2O2 for 100 g of solution.The titre expressed as the volumeof oxygen (in litres) freed by 1 litreof solution.According to the reaction (1) it ispossible to write:

Titre (in volumes) =(10 * titre (in %) / d) * 11.2 / 34

34 = molar weight of H2O2

11.2 = volume of ½ mole of O2under normal pressure and tem-perature conditionsd = H2O2 density

If density is supposed equal to 1:Titre (in volumes) =

Titre (in %) * 3.294


MC3051Pt-9 Metal Electrodecombined, platinum (part no.E31M003) with CL114 cable (partno. A94L114

25% v/v H2SO4 solution in distilledwaterDilute 250 ml of concentrated sul-phuric acid in 750 ml of distilledwater. This operation is veryexothermic, so perform the dilu-tion very slowly and respect labo-ratory safety regulations. Let thesolution cool to room temperature.This solution is approximately 9N or4.5M.

KMnO4 solution (M/50 or 0.02M;note this solution is N/10)Using a volumetric flask, dilute3.160 g of potassium permanga-nate in 500 ml of distilled water,add 10 ml of 25% sulphuric acidsolution, leave to cool to roomtemperature and complete to1000 ml with distilled water.Store in a brown flask.Note that this solution is commer-cially available.

Distilled water

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Inflection DetectionSettings

Burette volume: 25 ml(see Working range)

Stirring speed: 650 rpm(see Stirring)

Working mode: mVStart timer: 15 sMaximum volume: 25 mlStop point: 1250 mVDirection: Increasing mVPredose: 10.0 ml

(see Predose note)Minimum speed: 0.2 ml/minMaximum speed: 4.00 ml/minSmoothing parameter: 5

Minimum ordinate: 750 mVMaximum ordinate: 1100 mVStop at last IP: YES

Sample unit: gSample amount: 11

(see Sample amount note)Dilution: YES

(see Working range)Final dilution amount: 1000 mlAliquot: 10 ml

Result number: 1Result: %Molar weight: 34 g/molReaction: 5Smp + 2Titr

Equation number: 1Equation unit: conc. (volumes)Equation: R1*3.294

(see Equation note)

Procedure

Dilute the sample according to thedilution factor described underWorking range.

In the titration beaker pipette therecommended sample aliquot(see Working range).

Add a sufficient quantity of dis-tilled water and 10 ml of the 25%v/v sulphuric acid solution.

Hydrogen Peroxide Determination (by manganimetric titration)

Immerse the combined platinum/reference electrode.

Run the titration.

Results

Results can be expressed in twodifferent units

R(%) = (5 * Ctitr * Vtitr / 2 * Vsmp) * (34/10)

5 and 2 = Reaction coefficientsCtitr = Titrant concentrationVtitr = Used titrant volumeVsmp = Used sample volume34 = Molar weight of H2O2

10 = factor to express result as a %

R(volumes) = R(%) * 3.294 / d

d = Sample density (in g/ml or kg/l)

Experimental results on com-mercial hydrogen peroxide4 determinationsResult as a %Mean: 29.75%Standard deviation: 0.022%Result in volumesMean: 89.09 vol.Standard deviation: 0.066 vol.

Working range

Using a 25 ml burette and ac-cording to the expected concen-tration of the hydrogen peroxide,refer to the following table tochoose the dilution factor andsample aliquot for the titration:

% w/w Titre (vol.)* Molarity* F. dilution Aliquot

6 19.8 1.8 10 5 ml

30 99 8.8 100 10 ml

40 130 11.8 200 10 ml

(*) Approximate value with d = 1

Notes

Sample amount10 ml are pipetted and weighed.

Stirring speedUse a sufficiently high stirringspeed to allow the oxygen bubblesgenerated during the reaction toleave the solution.

ProcedureEnsure you add sufficient acidsolution to obtain a well-shapedtitration curve.

PredoseThe predose function can be usedto save time. Modify this volumeaccording the expected volume oftitrant

EquationIf H2O2 density is known modifyto the equation as follows

Equation = R1*3.924/d

d = H2O2 density

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Direct curve

Curve

mV

ml12 16

1200

1000

800

201814

Hydrogen Peroxide Determination (by manganimetric titration)

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Dissolved Oxygen in Water

Introduction

Determination of dissolved oxygen(DO) is essential in water analysis,as oxygen is required for survivaland growth by many organisms.For this determination, 2 standardsare most commonly used basedon the same procedure but usingdifferent reagent concentrations.

Principle

The principle used is a modifiedWinkler titration with a 3-stepanalysis.Step one: reaction between dis-solved oxygen and divalent man-ganese Mn2+ according to

O2 + 4Mn2+ + 8OH- + 2H2O 4Mn(OH)

3

Step two: reduction of Mn(OH)3 by

I- in acidic media according to

4Mn(OH)3 + 4I- + 12H+

4Mn2+ + 2I2 + 12H

2O

Step three: titration of I2 using

sodium thiosulphate according to

2I2 + 4S2O32- 4I- + 2S4O6

2-

At the end, 1 molecule of O2corresponds to 4 molecules ofS2O3

2-

The titration of I2 by S

2O

32- can be

an end point titration using imposedcurrent potentiometry and a twoPt-Pt wire electrode or an inflection

point titration with continuous ad-dition mode.


The reagent concentrations varydepending on the standard used(see table):

KI solid state (for titrant calibration)Distilled water

European standard US standard

SOL 1 MnSO4, H2O SOL 1 MnSO4, H2O380 g/l in water 364 g/l in water

SOL 2 KIO3 SOL 2 KH(IO3)2

0.3567 g/l in water 0.8124 g/l in water(1/600 mol/l = 0.00167 mol/l = 0.01 eq/l) (0.0021 mol/l)

(for titrant calibration) (for titrant calibration)

SOL 3 Na2S2O3, 5H2O SOL 3 Na2S2O3, 5H2O2.48 g/l in water (0.01mol/l) 6.205 g/l in water (0.025 mol/l)0.4 g/l NaOH 0.4 g/l NaOH(Titrant) (Titrant)

SOL 4 H2SO4 50% vol./vol. in water SOL 4 H2SO4 concentrated

SOL 5 SOL 5 A BNaOH 35 g NaOH 480 g or NaOH 500 gNaI 27 g NaI 750 g NaI 135 gNaN3 1 g NaN3 10 g NaN3 10 gIn 100 ml of water In 500 ml of water In 1000 ml of water

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Electrode for end point titrationMC231Pt2 Metal Electrode withtwo Pt-Pt wires with adapter partno. A94P801 (BNC 2 banana) orM241Pt2-8 Metal Electrode.

Electrode for inflection pointtitrationMC3051Pt-9 Metal Electrode,combined platinum/reference(part no. E31M003) with cablepart no. A94L114.

End Point Titration settings

Burette volume: 25 mlMaximum volume: 25 mlWorking mode: mV with i = 1µA (DC)Stirring speed: 600 rpm

Number of end points: 1End point: 200 mVStirring delay: 40 secondsMinimum speed: 0.1 ml/minMaximum speed: 2.5 ml/minTitration: Increasing potentialProportional band: 150 mVEnd point delay: 5 seconds

Sample unit: mlDilution: YESSample amount:: 300Final dilution amount: 302Aliquot: 200

Result1Unit: mg/lReaction: 1 sample + 4 titrantMolar weight: 32 g/mol


Burette volume: 25 mlMaximum volume: 25 mlStirring speed: 600 rpmStirring delay: 10 sStop point: 120 mVSmoothing parameter: 5Inflection point number: 1Minimum speed: 0.2 ml/minMaximum speed: 5 ml/minDirection: Decreasing mVStop at last IP: YES

Inflection 1Min. ordinate: 200 mVMax. ordinate: 450 mV

Sample unit: mlDilution: YESSample amount: 300Final dilution amount: 302Aliquot: 200

Result1Unit: mg/lReaction: 1 sample + 4 titrantMolar weight: 32 g/mol

Procedure

Set up the Titration Manager withSOL 3 as titrant.

Connect the two Pt/Pt wire orcombined platinum/referenceelectrode.

Enter the titrant concentration(use mol/l or mmol/l) in the Titra-tion Manager.

Add 1 ml of SOL 1 and 1 ml ofSOL 5 to the sample collected in abottle (generally 300 ml).

Stopper the bottle securely andmix the solution by turning thebottle upside down several times.

Leave the solution. When precipi-tate has settled sufficiently (half ofthe bottle) add 1 ml of SOL 4 andstopper the bottle. Mix the solutionby turning the bottle upside downuntil dissolution is complete.

Pipette 200 ml of treated sample.


Start method by pressing theRUN key.

Results

Expressed as mg/l of O2 as ti-trant concentration is expresseden mol/l

R = V(titr) * C(titr) * 32 * 1000 / V(smp) * 4


- V(titr) = Volume of titrant in ml- C(titr) = Concentration of titrantin mol/l- 32 = molecular weight of oxygen- V(smp) = Actual sample volumeused for titration- 4 = Factor according to the factthat 1 molecule of O

2 corresponds

to 4 molecules of S2O

32-

For a result in mg/l of O2You need to take into accountthe dilution of the sample byreaction reagents as indicatedin the Titration Manager settings

3 determinations on a watersampleMean: 15.03 mg/lStandard deviation: 0.108 mg/lRelative standard deviation: 0.7%

Working range

Note that according to the above-mentioned formula, for 200 ml ofsample and with a titrant con-centration of 0.025 mol/l:

1 ml of titrant corresponds to1 mg/l of DO

The experimental limit of themethod is about 2 mg/l.

Notes

SOL 5B is used for samples thatare not highly saturated and SOL5A for "supersaturated" samplesAddition of NaN

3 eliminates inter-

ference from NO2- ions

For other modifications necessarydue to interference, refer to yourlocal standards.

Titrant calibration

If necessary, you can calibrate thesodium thiosulphate solution usingthe procedure described in appli-cation note TTEP01.08MIN (addi-tion of solid state Kl and concen-trated acid before titration).

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With KIO3 (European standard)In this case, 1 molecule of KIO

3corresponds to 6 molecules ofNa

2S

2O

3 according to

IO3- + 5I- + 6H+ 3I2 + 3H2O

3I2 + 6S

2O

32- 6I- + 3S

4O

62-

Pipette 10 ml of SOL 2, add 1 g ofKI, 50 ml of distilled water and 5 mlof sulphuric acid 50% v/v solution.

Enter as standard amount: 10Standard unit: mlStandard conc.: 1.67 mmol/l (mM)

Result unit: mmol/l (mM)Coefficients: 1 standard and 6 titrant

Depending on the titrant andstandard concentrations indicatedabove, around 10 ml of sodiumthiosulphate solution is required.

With KH(IO3)2 (US standard)In this case, 1 molecule ofKH(IO

3)

2 corresponds to 12

molecules of Na2S

2O

3

Pipette 10 ml of SOL 2, add 1 g of KI,50 ml of distilled water and fewdrops of concentrated sulphuricacidEnter as standard amount: 10Standard unit: mlStandard conc.: 2.1 mmol/l (mM)

Result unit: mmol/l (mM)Coefficients: 1 standard and 12 titrant

Depending on the titrant andstandard concentrations indicatedabove, around 10 ml of sodiumthiosulphate solution is required.

Bibliography

International standard ISO5813.1983European standard EN25813.1992Standard methods for water andwastewater 18th edition (1992)4-98 part 4500

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Iodine Value of Animal andVegetable Fats and Oils

(EN ISO 3961 (1999) and ISO 3961 (1996))

Introduction

The iodine value of animal andvegetable fats and oils measuresthe amount of -C=C- (doublebonds) present in the product. Theresult is expressed as g of iodine(I

2) per 100 g of sample; the molar

weight of I2 is 253.8 g/mol. Instead

of I2, ISO 3961 and EN ISO 3961

standards use Iodine chloride (I Cl)in acetic acid solution, also knownas Wijs solution, for this determi-nation.

ISO and EN ISO standards usethe reaction of the sample with anexcess of Wijs solution followed bydetermination of excess of Wijssolution using a redox titrationwith sodium thiosulphate.As indicated in standardISO 3961, potentiometric deter-mination of the equivalencepoint can be used.

Summary

The iodine value determinationinvolves a three-step operation:

1) Reaction of sample with Wijssolution in excess according to

R-C=C-R + I Cl R-CI-CCl-R

2) Reaction of the excess of Wijssolution with potassium iodideaccording to

I Cl + I- I2 + Cl-

3) Determination of the amount ofreleased iodine according to

I2 + 2S

2O

32- 2I- + S

4O

62-

According to this three-step op-eration, the titration is a back titra-tion with a blank.This titration is run according toinflection detection with continuousaddition of the titrant with a com-bined platinum/reference electrode,but it is also possible to work witha pre-set end point titration.


MC3051Pt combined platinum/reference electrode (part no.E31M003)CL114 connecting cable (part no.A94L114)OrM241Pt2-8 (part no. E32M002) ora M231Pt-2 Metal Electrode (partno. E32M001) with adapter partno. A94P801.

Wijs solution 0.1M (see notebelow)This solution is commerciallyavailable (e.g. part no. 35 071from Sigma Aldrich)

Titration solvent: Mix the samevolumes of cyclohexane and gla-cial acetic acid.

Potassium iodide solution: Dis-solve 100 g of potassium iodide in1000 ml of pure water.Store the solution in a brown bottleavoiding oxidation of the iodide ion.

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Sodium thiosulphate solution 0.1 mol/(or 0.1N)Na

2S

2O

3, 5H

2O has a molecular

weight corresponding to248.181 g/mol.To prepare a 0.1 equivalent/l (or0.1 mol/) sodium thiosulphatesolution; dissolve 24.8181 g ofNa

2S

2O

3, 5H

2O in 500 ml of

freshly distilled water (or freshlyboiled and cooled deionised wa-ter) and 2 or 3 drops of CHCl

3 and

complete to 1000 ml using a volu-metric flask.Wait for one day and filter the so-lution if necessary (precipitation ofsulphur can occur).Stock the solution in a brownglass flask.Look at the solution from time totime and filter/standardise again ifnecessary.This solution is also commerciallyavailable.

Distilled or deionised water


Back titration with blankBurette volume: 25 ml or 50 ml

(see "burette capacity" below)Stirring speed: 700 rpm

Working mode: mVStart timer: 20 sec

Blank: YESMin. ordinate: 200 mVMax. ordinate: 300 mV

Predose until:(see "burette capacity" below)

Maximum volume: 25 ml or 50 mlStop point: 100 mVDirection: decreasing mVMinimum speed: 0.1 ml/minMaximum speed: 5.00 ml/minSmoothing parameter: 5

Back Titration: MANUAL(see "back titration" below)

Excess reagent: Wijs solutionExcess volume: 20 mlExcess titre: 0.1

Inflection1:Minimum ordinate: 200 mVMaximum ordinate: 300 mVStop at last IP: YES

Sample unit: gSample amount:

(see "working range" below)Dilution: NO

Result: %Molar weight: 253.8 g/molExcess: 2 Smp + 2 Exc

(see "result" below)Reaction: 1 Exc + 2 Titr

Procedure (see notes)

For blankFor blank determination, preparea solution in the same way asindicated below but without asample.

For sample Weigh the recommended amountof oil (see "working range")Add the recommended volume oftitration solvent (20 or 25 ml).Add 20 ml (10 ml can sometimesbe sufficient) of Wijs solution (see"Wijs solution" and "burettecapacity").Mix the solution and stopper thebeaker (or the conical flask).Leave the solution in the dark for1 or 2 hours (refer to local stand-ards) until the first step of the re-action is complete. Remember thereaction time depends on the na-ture of the sample and excess ofWijs solution if results are to bereproducible.

Iodine Value of Animal and Vegetable Fats and Oils (EN ISO 3961 (1999) and ISO 3961 (1996))

Next add 20 ml of the potassiumiodide solution and 100/150 ml ofdeionised water.If the procedure uses a conicalflask with a ground glass stopper,it is possible to pour the solutioninto a beaker just before the titra-tion, using deionised water torinse the flask.Titrate the blank followed by thecorresponding sample.

Results

As the result is generally ex-pressed in g of I2 per 100 g ofsample; according to the reac-tions, the Titration Manager calcu-lates the result according to:

R = (Vbl - Vsmp) * Ctitr * 253.8 / 2 * Wsmp * 10

Vbl = Titrant volume for blank in ml

Vsmp

= Titrant volume for sample in mlC

titr = Titrant concentration in mol/l

253.8 = Molar weight of I2

Wsmp = Sample weight in g2 = Stoechiometric factor of thereactions (1 mole of I Cl corre-sponds to 1 mole of I2 that corre-sponds to 2 moles of S

2O

32- )

10 = Factor expressing result in %

For determination on old peanutoilIodine number: 80 g/100 g

Working range

Depending on the expected iodinevalue, look at the following table todetermine the correct sampleamount.

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Iodine Value of Animal and Vegetable Fats and Oils (EN ISO 3961 (1999) and ISO 3961 (1996))

mV

ml

5 10

310

240

15 20

mV

ml

2 4

320

220

10 126 8

270

Blank - Continuous IP mode

Iodine value in % Sample amount in g Solvent in ml Vbl - Vsmp in ml

<1.5 15 25 17

1.5 - 2.5 10 25 12 - 19

2.5 - 5 3 20 6 - 12

5 - 20 1 20 4 - 16

20 - 50 0.4 20 6.5 - 16

100 - 150 0.13 20 10 - 15

150 - 200 0.1 20 12 - 16

It is important to have a sample amount that corresponds to thevolume of the Wijs solution.The quantity of Wijs solution consumed by the sample should beclose to 50% of the total amount of Wijs solution added.

Notes

Wijs solutionThis solution is inflammable andcorrosive.Work under a hoodNever pipette this solution di-rectly with the mouth, alwaysuse a pro-pipette.Always consult the safety datasheet available from the productsupplier before handling.

Burette capacity and maximumvolumeAccording to the reaction betweenI Cl and I- and titration of I

2 with

S2O

32-, if you use 20 ml of I Cl 0.1M,

the blank determination theoreti-cally needs 40 ml of S

2O

32- 0.1M.

This should be taken into accountwhen choosing the burette capac-ity (25 or preferably 50 ml), themaximum volume and the possiblepredose volume.Use of the predose may be man-datory in continuous IP titrationwith a 25 ml burette capacity andsaves time in end point titration

Back titrationAs it is necessary to wait 1 or 2hours for a complete reaction, donot use AUTOMATIC back titration.

ProcedureAs the titration medium is a two-phase medium, it is advisable touse large diameter beakers and astirring speed of around 700 rpmin order to obtain efficient mixingof the two phases. Otherwise,some iodine may stay in the or-ganic phase (becoming light violetcoloured) giving a false result.According to some publications, itis possible to shorten the reactiontime by adding 10 ml of 2.5%mercuric acetate [(CH

3COO)

2Hg]

solution in water as catalyst afterthe Wijs solution.

ResultFor a back titration, the TitrationManager asks for identical coeffi-cients for Sample and Titrant.

END POINT TITRATIONAs indicated in application noteTTIP-EP02-01AFD (Iodometrictitration of Vitamin C); it is possibleto work with a M241Pt2-8 MetalElectrode (part no. E32M002) or aM231Pt-2 Metal Electrode (partno. E32M001) with adapter partno. A94P801, using imposed cur-rent potentiometry.

In this case, the Titration Managersettings should be modified asfollows:

Working mode: mV i>0Current value: 1 µADirection: Increasing mVMinimum speed: 0.2 ml/minMaximum speed: 2.00 ml/min

Number of end points: 1End point: 200 mVProportional band: 190 mVEnd point delay: 5 sec

The other settings are similar tothose already described.

Curves

Sample - Continuous IP mode

REDOX TITRATIONS Introduction

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