DOI: 10.2478/s11532-007-0013-0Research article

CEJC 5(2) 2007 455–465

Ion-pair chromatographic monitoringof photographic effluents

Giedre Kesiunaite1, Birute Pranaityte1, Audrius Padarauskas1∗,Arvydas Dikcius2, Romas Ragauskas2

1 Department of Analytical and Environmental Chemistry,Vilnius University,

LT-03225 Vilnius, Lithuania2 Institute of Chemistry,

LT-01108, Vilnius, Lithuania

Received 21 November 2006; accepted 4 January 2007

Abstract: Ion-pair chromatographic technique was developed for the rapid and simple determinationof the main contaminants (bromide, iodide, sulphite, thiosulphate, thiocyanate, iron(III)-EDTA chelate,free EDTA, hydroquinone and phenidone) in spent photographic solutions. Free EDTA was convertedinto stable Ni(II)-EDTA chelate prior to analysis. The optimal mobile phase conditions were establishedby varying the concentrations of tetrabutylammonium (TBA) phosphate and acetonitrile, pH and ionicstrength. Separation of five inorganic anions, two metal chelates and two neutral compounds wasaccomplished in about 30 min using a mobile phase containing 7.5 mmol/L TBA-phosphate, 10 mmol/LNaCl (pH 6.5) and 20% (v/v) acetonitrile. The detection limits (UV detection at 210 nm) ranged from 0.4µmol/L for phenidone to 8 µmol/L for sulphite with a linearity of 2–2.5 orders of magnitude. The methodwas applied to the rapid monitoring of spent photographic solutions before and after decomposition. Therecovery tests established for two samples were within the range 95–103%.c© Versita Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved.

Keywords: Ion-pair chromatography, anions, neutral compounds, photographic effluents

1 Introduction

The increasing use of black and white and color photography is leading to an increase in

the problem of contaminated waste solution. A typical photographic process involves basi-

cally two steps: developing and fixing [1]. The main components present in a photographic

∗ E-mail: audrius.padarauskas@chf.vu.lt

456 G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465

developer are the developing agent (hydroquinone (1,4-dihydroxybenzene) and phenidone

(1-phenyl-3-pyrazolidone)), an antioxidant (sulfite) and an alkaline buffer (potassium car-

bonate). The fixing baths usually contain thiosulfate, sulfite, thiocyanate, free ethylene-

diaminetetraacetic acid (EDTA) and FeEDTA− complex. In addition, the effluents from

used baths may also contain large amounts of Br− and in some cases I− anions which

appear during the photofinishing process. In most photolaboratories the ecologically

harmful spent photographic solutions accumulate. In order to minimize unwanted envi-

ronmental contamination, these solutions should be collected and decomposed. In the

last decade various techniques have been investigated for this purpose [2–6]. The main

problem of such investigations is the need for simple but rapid monitoring of contami-

nants before and during their decomposition. Because of the different chemical properties

of these compounds the monitoring of spent photographic solutions is labor-intensive as

well as time-consuming.

In the last few years, capillary electrophoresis (CE) has been successfully introduced

for the analyses of various photographic solutions [7–14]. However, the determination of

fast (e.g., Br−, S2O2−3 ) and less mobile (free EDTA, FeEDTA−) anions together with neu-

tral compounds (hydroquinone, phenidone) using CE technique requires entirely different

conditions and cannot be performed in a single run.

Currently, a variety of high-performance liquid chromatography (HPLC) techniques

can be used for the analysis of organic and inorganic species [15]. There are only a

few studies dealing with the HPLC analysis of photographic solutions. Conventional

reversed-phase HPLC with UV detection was used for the determination of common

black-and-white as well as colour [16] or X-ray film [17] developing agents in photographic

baths. HPLC-mass spectrometry was applied to determine the degradation products of

the developing agents in photographic effluents [18, 19] and to characterize toxic organic

pollutants in colour photographic wastewaters during their chemical degradation [20].

However, this HPLC mode is hardly suited for the analysis of highly hydrophilic charged

analytes.

The most common method used for anion analysis in the last two decades is ion

chromatography (IC) [21], but the use of ion-exchange stationary phases preclude the

possibility to determine neutral compounds together with inorganic anions.

An alternative to the conventional IC method is the ion-pair chromatography (IPC)

[22], wherein a mobile phase containing a hydrophobic counter-ion is used with a reversed-

phase stationary phase. Generally, the use of this kind of stationary phase gives better

efficiencies than those obtained with conventional ion exchangers. Moreover, in the case

of complicated samples, IPC offers several advantages over IC, including more mobile-

stationary phase parameters that can be adjusted for optimization of the separation,

capability to analyze samples containing both ions and neutral species, reduced analysis

time together with better separation selectivity [23].

The main aim of this study was to evaluate the IPC technique for a rapid and simple

monitoring of spent photographic solutions.

G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465 457

2 Experimental

2.1 Instrumentation

The HPLC instrumentation consisted of a Waters Model 501 high-pressure pump, an

injection valve equipped with a sample loop of 20-µL and a Waters Lambda-Max Model

481 variable wavelength UV detector set to absorb at 210 nm. The results and data were

collected and plotted on a plotter/integrator SP 4290 (Spectrophysics, San Jose, CA,

USA). IPC separations were performed on a 5 µm AscentisTM C18 (150×4.6 mm i.d.)

column (Supelco, Bellefonte, PA, USA). The mobile phase flow rate was 0.5 mL/min.

2.2 Reagents and solutions

All mobile phases and standard solutions were prepared using doubly distilled helium

degassed water. HPLC-grade acetonitrile was purchased from Merck (Darmstadt, Ger-

many). Tetrabutylammonium (TBA) hydroxide solution (40% in water) was obtained

from Fluka Chemie GmbH (Buchs, Switzerland). All other reagents were of analytical-

reagent grade obtained from Aldrich (Milwaukee, WI, USA). Stock solutions (10 mmol/L)

of the analytes were prepared in water. Hydroquinone and phenidone standard solutions

were prepared just before use. Sodium sulfite stock solutions were prepared daily and

standardized by iodometric titration. Metal complexes with EDTA were prepared by

direct mixing of equimolar amounts of metal and EDTA standard solutions. All working

solutions were prepared before use by suitable dilution. Initial 0.1 mol/L TBA-phosphate

solution was prepared by neutralization of appropriate amount of tetrabutylammonium

hydroxide with H3PO4 to desired pH.

All mobile phase and sample solutions were filtered through a 0.45 µm nylon 66

membrane filter (Supelco, Bellefonte, PA, USA) and degassed by ultrasonication.

2.3 Sample preparation

Anodic oxidation test was performed in a teflon cell (10 mL) using a boron doped diamond

anode (0.8 cm2) and Pt cathode. Stirring was implemented by turning plastic bar inserted

in the cell. Oxidation was carried out for 3 h 20 min at a constant current of 50 mA.

The sample solution was filtered through a 0.45 µm membrane filter. After this, an

aliquot of the sample solution (0.25 mL) was placed in a 25 mL volumetric flask and

0.125 mL of 10 mmol/L (NH4)2MoO4 and 0.50 mL of 10 mmol/L NiCl2 were added.

Finally, the solution was adjusted to final volume with mobile phase and analyzed.

458 G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465

3 Results and discussion

3.1 Derivatization of free EDTA

As mentioned previously , the major components of spent photographic solutions are

Br−, I−, S2O2−3 , SO2−

3 , Ag(S2O3)3−2 , SCN−, FeEDTA−, free EDTA, hydroquinone and

phenidone. Silver from such solutions is recovered electrolytically. All these compounds

except free EDTA exhibit relatively strong absorbance in the UV range 200-220 nm.

Consequently, the determination of all these nine analytes in a single run can be performed

only after derivatization of free EDTA into a UV-absorbing derivative. Most of the

derivatization techniques are based on the complexation of EDTA with Fe3+ cation into

UV-absorbing, negatively charged chelate [24, 25]. However, the use of Fe3+ ions in

our system is complicated because spent photographic solutions already contain large

amounts of FeEDTA− chelate. Consequently, the determination of free EDTA using Fe3+

requires at least two separate runs of the same sample: one before and the other after

the derivatization. On the basis of our previous work [7], Ni2+ was selected in this study.

This cation forms doubly charged chelate with EDTA stable enough for derivatization

(logK = 18.5) which also has relatively strong UV absorption below 220 nm.

In order to determine whether an excess of Ni2+ causes a decomposition and/or pre-

cipitation of other analytes present in the real samples, various amounts of Ni2+ chloride

(from 0.5 to 5 mmol/L) were added to standard solution of each analyte (0.5 mmol/L)

and the analyte peak areas were measured and compared. No statistically significant de-

crease in the peak areas for all analytes was observed with increasing Ni2+ concentration

up to about 1 mmol/L.

3.2 Chromatographic separation

Tetraalkylammonium salts have been widely used as ion-pairing reagents for the sepa-

ration of anionic compounds. In studies of the determination of the inorganic anions

the tetrabutylammonium (TBA) ion has been the most popular ion-pairing reagent [22].

Consequently, TBA-phosphate was selected as an ion-pairing reagent in this study. In or-

der to establish the optimal concentration of TBA in the mobile phase for the separation

of the analytes studied, various amounts (from 1 to 10 mmol/L) of TBA-phosphate were

tested in acetonitrile-water (20:80 v/v) mixtures. The pH of the aqueous TBA-phosphate

solution was kept constant in these experiments at 6.5. The results obtained are shown in

Fig. 1. As can be observed, with increasing TBA-phosphate concentration in the mobile

phase from 1 to about 5-6 mmol/L the dynamic ion-exchange capacity of the stationary

phase and, consequently, the retention of anionic analytes increase. As the concentra-

tion of the ion-pairing reagent was increased further, there was a clear leveling off in

retention, followed by significant reductions in retention, particularly for thiocyanate and

thiosulphate. Thiosulphate was particularly sensitive to TBA-phosphate concentration,

as selectivity changed from thiosulphate > iodide > thiocyanate at 1 mmol/L TBA-

G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465 459

phosphate, to thiocyanate >iodide > thiosulphate at 10 mmol/L TBA-phosphate. In

general, the trends shown in Fig. 1 are again typical of an ion-pair mechanism with the

maximum retention being achieved at the point where stationary phase surface becomes

saturated with the ion-pairing reagent. After this point further addition of the reagent

to the mobile phase causes a reduction in retention due to the increased concentration of

the counter-ion, in this case phosphate.

Fig. 1 Effect of TBA-phosphate concentration on retention times. Mobile phase: TBA-

phosphate (pH 6.5), 20% (v/v) CH3CN; flow rate: 0.5 mL/min; UV detection at 210 nm.

1 – hydroquinone; 2 – phenidone; 3 – Br−; 4 – SO2−3 ; 5 – FeEDTA−; 6 – NiEDTA2−; 7 –

S2O2−3 ; 8 – I−; 9 – SCN−.

As expected, the effect of TBA-phosphate concentration on the retention of neutral

analytes (hydroquinone and phenidone) was negligible.

However, it was clear from the results obtained that there was a large difference in

retention times shown between what can be termed the more hydrophilic anions, sulphite,

bromide, FeEDTA− and NiEDTA2−, and the less hydrophilic anions, iodide, thiosulphate

and thiocyanate. Therefore, three other parameters were chosen for optimization, namely

the mobile phase pH and ionic strength, and the concentration of the acetonitrile.

The effect of mobile phase pH on analyte retention was studied over the range of 4-7.

Varying pH had little or no effect on improving the separation selectivity. Only sulphite

retention was slightly increased with pH because of the deprotonation at higher pH. The

retention times of other analytes decreased gradually with the increasing pH values. It

would appear, therefore, that in our system, variation of mobile phase pH range has no

practical application to modification of the separation selectivity.

Increased acetonitrile concentration (from 20 to 40% v/v) greatly accelerated elution

of the both anionic and neutral analytes and the concentration in the range 20-25% (v/v)

460 G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465

provided the best resolution.

Fig. 2 shows the effect of NaCl concentration on retention times. The results show

that the ionic strength has little influence on the retention of hydroquinone and phenidone

which leads one to conclude that this parameter does not significantly affect the adsorp-

tion capacity of the stationary phase. On the contrary, increasing the salt concentration

in the mobile phase leads to a significant decrease in the retention of all tested anions.

Increase in the chloride concentration provided by increase in the ionic strength salt re-

duces analyte anion retention by mass action by competing with the analytes for the

ion-exchange sites. In addition, the ionic strength effect was more pronounced for the

metal-EDTA chelates indicating that, most likely, this parameter also modifies the com-

plexation equilibrium.

Fig. 2 Effect of NaCl concentration on retention times. Mobile phase: 7.5 mmol/L

TBA-phosphate (pH 6.5), 20% (v/v) CH3CN. Other conditions as in Fig. 1.

From the above optimization experiments, a mobile phase of acetonitrile–water (20:80,

v/v) containing 7.5 mmol/L TBA-phosphate (pH 6.5) and 10 mmol/L NaCl was selected

as optimal. These conditions were found to provide the best resolution of the test mixture

of nine analytes in the shortest total run time of 30 min. A chromatogram obtained under

optimized conditions is shown in Fig. 3.

3.3 Analytical performance

In the case of samples containing large number of the analytes the use of an internal

standard is perhaps the best choice for quantitative determinations. In this study we

have selected molybdate anion (as its ammonium salt) as the internal standard for both

anionic and neutral analytes. This anion is well suited for the purpose because it elutes

G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465 461

Fig. 3 Optimized separation of nine compounds. Mobile phase: 7.5 mmol/L TBA-

phosphate, 10 mmol/L NaCl (pH 6.5), 20% (v/v) CH3CN; flow rate: 0.5 mL/min; UV

detection at 210 nm. Peaks: 1 – hydroquinone; 2 – Br−; 3 – phenidone; 4 – SO2−3 ; 5 –

FeEDTA−; 6 – NiEDTA2−; 7 – S2O2−3 ; 8 – I−; 9 – SCN−.

in the free space just before thiosulphate, does not react with the analytes and exhibits

relatively high absorbance at 210 nm. In addition, the photographic effluents do not

contain molybdate ions. A 0.05 mmol/L concentration of internal standard was used in

all determinations.

Reproducibilty of the experiments was confirmed by performing six consecutive runs

with standard solutions containing 0.1 mmol/L of each analyte. The relative standard

deviations (RSD) of retention times and relative peak areas were in the range from 0.2%

for Br− to 0.5% for SO2−3 and from 0.6% for I− to 3.8% for phenidone, respectively. The

significantly higher relative peak area RSD value for phenidone probably can be explained

by the higher oxidation ability for this analyte.

The day-to-day precision of the method was evaluated for a concentration of 0.1 mmol/L

of each analyte by making repeated analyses on different days. Standard mixtures of the

analytes were prepared each day and analyzed through six replicates during three days.

The obtained RSDs of retention times and relative peak areas were less than 0.8% and

4.5%, respectively.

The linearity of the method was tested by preparing a calibration curve for each

analyte with six points. Each concentration level (up to 2.0 mmol/L) was injected three

times. Detection limits were calculated using peak height equivalent to three times the

baseline noise. These results are summarized in Table 1. Detection limits are low enough

for the method to be useful for the monitoring of spent photographic solutions before and

during their decomposition.

462 G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465

Table 1 Linearity data and detection limit values.

Analyte Linear range, R2 Detection limit,µmol/L µmol/L

Hydroquinone 7.5 – 500 0.997 1.8Phenidone 1.5 – 500 0.998 0.4Br− 7.5 – 1500 0.999 2.5SO2−

3 25 – 1500 0.996 8.0FeEDTA− 1.5 – 500 0.999 0.5Free EDTA 4.0 – 500 0.999 1.6I− 2.5 – 1000 0.999 0.8S2O2−

3 7.5 – 1500 0.998 2.3SCN− 20 – 1500 0.998 6.5

Table 2 Results of the IPC determination of main contaminants in photographic effluents

(n = 3).

Sample Analyte Found Added Found total Recovery(mmol/L) (mmol/L) (mmol/L) (%)

Before Hydroquinone 0.81 2.00 2.72 95.5decomposition Phenidone 1.45 2.00 3.42 98.5

Br− 18.6 5.00 23.7 102.0SO2−

3 5.61 5.00 10.4 95.8FeEDTA− 6.53 5.00 11.6 101.4Free EDTA 2.30 5.00 7.43 102.6

I− ND 5.00 5.05 101.0S2O2−

3 68.3 10.0 78.1 98.0SCN− 14.8 10.0 24.7 99.0

After Hydroquinone ND 1.00 0.95 95.0decomposition Phenidone ND 1.00 0.99 99.0

Br− 4.52 2.00 6.54 101.0SO2−

3 ND 5.00 4.78 95.6FeEDTA− 1.26 2.00 3.30 102.0Free EDTA ND 2.00 1.97 98.5

I− ND 2.00 2.03 101.5S2O2−

3 ND 2.00 2.05 102.5SCN− ND 5.00 4.89 97.8

ND – not detected.

3.4 Sample analysis

To illustrate how the methodology developed here has real application potential, the

method was briefly applied to the determination of main contaminants in photographic

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effluent sample before and after decomposition by anodic oxidation. To establish an

optimal amount of Ni2+ required for complete complexation of free EDTA various con-

centrations of Ni2+ were added to a 1:100 diluted sample and the amount of NiEDTA2−

chelate was measured. The obtained results showed that at Ni2+ concentrations higher

than 0.1 mmol/L, no statistically significant increase in the amount of NiEDTA2− was ob-

served indicating the completeness of the derivatization reaction. Therefore, 0.2 mmol/L

NiCl2 was added to the samples in the assays.

Fig. 4 Chromatograms for a 1:100 diluted photographic effluent sample before (a) and

after (b) decomposition. IS – internal standard (MoO2−4 ). Other peaks and conditions as

in Fig. 3.

The chromatograms for a 1:100 diluted photographic effluent sample before and after

decomposition are compared in Fig. 4 (a) and (b). As can be seen, iodide was not

detected and only a relatively small (compared to expected value) amount of sulphite

was measured in the initial sample. This is not surprising, because iodide may be present

only in some photographic solutions, whereas sulphite as already mentioned is prone

to air oxidation. The sample pre-treatment stage only involves filtration of the sample

through a 0.45 µm pore filter, addition of an internal standard and NiCl2 and appropriate

dilution. A recovery study was carried out with two samples and the results are given

464 G. Kesiunaite et al. / Central European Journal of Chemistry 5(2) 2007 455–465

in Table 2. It can be seen in the table that the concentrations found were generally in

good agreement with the added concentrations, with recoveries between 95 and 103%.

Slightly lower recoveries for hydroquinone and sulphite may be most likely attributed to

the higher oxidation ability for these compounds. Phenidone possesses the property of

being regenerated by the hydroquinone, therefore in the presence of hydroquinone it is

significantly less prone to air oxidation. These results suggest that interferences by the

other matrix components are not significant.

In conclusion, the results obtained here show that the IPC technique proved to be

satisfactory for the monitoring of spent photographic solutions with simple sample prepa-

ration and with high speed compared with other analytical techniques.

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