Principles of ICP/MS with and without collision/reaction cell and High Resolution History of element...

JC Alvarez et coll., Chamonix, 21-26 mars 2011

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Principles of ICP/MS with and withoutcollision/reaction cell and High

Resolution

J.C. Alvarez

Pharmacology - Toxicology, University Versailles Saint-Quentin-en-Yvelines

Garches Universitary Hospital, France

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History of element testing

1960-1970 : Atomic Absorption SpectroscopyQualitative and quantitative determination of chemicalelements employing the absorption of optical radiation

necessary to atomize the sample in order to analyzeits atomic constituents

The two atomizers most commonly used:- 1960 : flame atomizer(F- Atomic Absorption Spectroscopy)

- 1970 : electrothermal atomizer usinggraphite tube (ET-AAS)


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Principle of AAS

wavelength

- AAS : Electrons of atoms from samples can be stimulated to achieve an excited state after absorbtion of a specific quantity of energy (λ: wavelength)

- Specific to a particular electron transition in a particular element- Radiation flux with or without sample in the atomizer is measured

(absorbance detector) element concentration

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Advantages and disadvantagesof AAS

- AAS with flame atomizer

- Easy to use, but not very sensitive, needs large sample quantities, long analysis time

- Needs regular cleaning of the burner

- Monoelement testing: only one element can bemeasured each time


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Advantages and disadvantagesof AAS

- AAS with electrothermal atomizer

- Much more sensitive

- Graphite tube has to be changed often: expensive

- Time consuming, because the use of a chemicalmodifier is often needed in order to stabilize the analyte at a pyrolysis temperature, needed to remove the majority of the matrix components

- Mono-element testing

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History of element testing (2)

- 1975 : Inductively Coupled Plasma - Atomic EmissionSpectroscopy (ICP-AES)


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Principles of ICP-AES

- Aqueous sample atomized with Ar gas into a hot plasma- Plasma (constituted by ionized argon) achieves temperatures

close to 7000°C organic matrix will be totally destructed- Plasma produces excited atoms and ions that emit

electromagnetic radiation at wavelengths characteristic of a particular element. The sample contains a mixture of elements. Therefore, a spectrum of light wavelengths isemitted simultaneously

- X elements measured simultaneously: multi-element analysis

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Advantages and disadvantagesof ICP-AES

- ICP-AES

- Less sensitive than ET-AAS, but it presents a larger concentration range

- Easy to use, needs less maintenance

- Relative few matrix effects, because of the hightemperature

- Allows multi-element testing


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History of element testing (3)

- 1983 : ICP-MS without collision cell

- 1995 : ICP-MS with collision cell

- 1990 : High Resolution -ICP-MS

1010

ICP-AES

ICP-MS HR-ICP-MS

Multi-elementtesting

Mono-element testing

F-AAS

ET-AAS

Sensitivity of the different methods

Typically used for measurement of mg/L, it may be extended to a few µg/L for some elements

Measurements in the low µg/L range can be carried out

Less sensitive than ET-AAS, but it allows multi-element testing and presents a larger dynamic range between g/L and µg/L

Used for measurements in the ng/L. It can be extended to pg/L using ICP-MS with High Resolution with a very important dynamic range between g/L and pg/L, allowing the quantification of different element with very different concentrations in the same sample


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Iron testing in blood

• F-AAS 5000 ppt (ng/L)• ET-AAS 100 ppt• ICP-AES 200-800 ppt

• ICP-MS without CC 200 ppt• ICP-MS with CC 8 ppt• HR-ICP-MS 0.8 ppt

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ICP-MS : principle

• It combines the easy sample introduction and quick analysis of ICP technology with the accurate and low detection limits of a mass spectrometer

• Separated into four main processes : sampleintroduction and aerosol generation, ionization by argon plasma source, mass discrimination and detection system


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ICP-MS : sample introduction

Sample is introduced by the way of a nebulizer, which aspiratessamples with argon under a highspeed, forming a fine mist

Aerosol passes into a spray chamber where larger droplets are removed

Process necessary to producedroplets small enough to bevaporized in plasma torch

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ICP-MS : Argon plasma and sample ionization

Aerosol moves into the torch body, and is mixed with more argon gas

A radio frequency is transmitted to the heatedargon gas

production of argon plasma flame at the torch

Hot plasma removes remaining solvent and causes - sample atomization ionization- sample atoms ionized but also excitedin hot plasma

phenomenon used in ICP-AtomicEmission Spectroscopy


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ICP-MS : Interface- Because atomization and ionization occur atatmospheric pressure, and MS detection needs a significant vacuum, an interface between ICP and MS components becomes crucial in creating vacuum environment for MS system

- An important pumping system is needed to continuously create a vacuum inside the spectrometer

- Several pumps are typically used to gradually reducepressure before the ion stream reaches the quadrupole

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ICP-MS : Mass spectrometer

- Ions are removed from plasma by a pumpedextraction system

- Ion beams are produced andfocused into a quadrupole

- At specific voltagesonly one particular ion is able tocontinue on its path betweenthe four rods, the others beingforced out of this path


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ICP-MS : detection

Ions detector in ICP-MS is usually a channeltronelectron multiplier

Ions leaving the quadrupoleare attracted to the interior of thecone surface

And electron amplification occursat each strike of the surface of the cone

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Performances

ICP-MS has the capability to scan all elementssimultaneously allowing rapid sample processing

Compared to ICP-AES:ICP-MS is more sensitive, able to detect ng/L with a larger concentration range


H

Li

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Na

Sc

Y

La

Ac

Ti

Zr

Hf

V

Nb

Ta

Ra

Cr

Mo

W

Mn

Tc

Re

Fe

Ru

Os

Co

Rh

Ir

Ni

Pd

Pt

Cu

Ag

Au

Zn

Cd

Hg

Ga

In

Tl

Ge

Sn

Pb

As

Sb

Bi

Te

Po

Br

I

At

Kr

Xe

Rn

Se

B

Al

C

Si

N

P S

F

Cl

Ne

Ar

O

Ce

Th

Pr

Pa

Nd

U

Pm

Np

Sm

Pu

Eu

Am

Gd

Cm

Tb

Bk

Dy

Cf

Ho

Es

Er

Fm

Tm

Md

Yb

No

Lu

Lr

He

1 - 10 ppt 100 ppt - 10 ppb> 10 ppb10 - 100 ppt0.1 - 1 ppt

Performances (2)

Many elements may be quantified at very low concentrations under 1 ppt (red) or under ten ppt (yellow).Only very few elements are quantified at concentrations above 10 ppt represented in green, pink, and brown

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Characteristics

ICP-MS needs less maintenance than ICP-AES: the increased sensitivity allows the use of sampledilution

less cleaning of the torch

One limitation when using ICP-MS is the presence of interferences. There are two kinds of interferences:

- Isobaric interferencesEx: interference of Kr82 on quantification of Se82

- Polyatomic interferencesEx: Ar40O16 polyatoms (created in plasma) interfere with the quantification of Fe56


Ar, Air

(O, N, C)

H2O, HNO3, Ca, Na, K, Mg, Cl, etc

ArAr, ArO,ArN, ArC, ArCa, ArNa, ArMg, ArCl, ClO, NO, CO, CaO, NaO, etc

Interferences produced during samplepreparation in plasma or coming from the matrix

AMU

ArN/54Fe

ArO/56Fe

The polyatomic interferences are coming from sample preparations with some ions such as calcium or sodium and from matrixes and Argon gas like the ArO polyatoms

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CRC is a device used in ICP-MS to removeinterfering ions through ion/neutral reactions

Chamber introduced before the quadrupole, to eliminate interferences

Interferring ions removed by injecting a collisional or reactive gas or a mixture of the two depending of the manufacturer destruction of polyatomic ions

Collisional gas usually used: HeReactive gases : ammonia, methane, oxygen or hydrogen

Solution : Collision/reaction cell


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Collision/Reaction Cell (CRC)

Fe56 and Ar40O16

Is there only one compound in the chromatogram peak ?Is the real value measured ?

Question: what is the real efficiencyof the destruction of the polyatomicions in the chamber?

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Solution ?

The solution should be to separate the differentpeaks of the different ions

When looking at the real mass of the twocompounds, the difference is very low:

Fe56 = 55.93494 AMU and Ar40O16 = 55.95729 AMU∆m = 0.02235 Atomic Mass Unit

The resolution into an ICP-MS quadrupole (definedby the ratio m/ ∆m) is always under 300, and depends of the mass measured

AMU = atomic mass unit


Resolution R = m/∆m

m=56, R<100 ∆m = 0.5Not enough to separateFe and ArO

For a mass of fifty six, the resolution into the ICP-MS is lower than one hundred allowing to differentiate a variation of mass around 0.5, which is not enough to separate Iron from ArO

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Interest of High Resolution ICP-MS

m=56 withR=10000∆m = 0.005

Fe56

Ar40O16

Ca40O16

totallyseparated

Only the high resolution ICPMS can separate the two compounds.For a mass of fifty six with a resolution into ten thousand, the variation of mass which is detectableis 0.005.As shown in this chromatogram, this resolution allows the separation of iron from ArO and alsofrom CaO.


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Conclusion : what prices ?

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• F-AAS 20-25 k€• ET-AAS 35-40 k€• ICP-AES 45-75 k€• ICP-MS without CRC 100-110 k€• ICP-MS with CRC 110-130 k€• HR-ICP-MS 400-450 k€

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Principles of ICP/MS with and without collision/reaction cell and High Resolution History of element...

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