Separation of chromium(III) and chromium(VI) by ion chromatography and an inductively coupled plasma mass spectrometer as element-selective detector

Due to its extensive use in industrial processes, large quantities of chromium compounds are discharged into the environment. Common approaches for the speciation of Cr employ the determination of Cr(VI) and total Cr. The focus of the present work was a separation of Cr(III) and Cr(VI) species, with a minimum of sample preparation, by keeping an eye on the more relevant and toxic Cr(VI). For the successful simultaneous separation of both chromium species we implemented a RSpak NN-814 4DP (PEEK, 4 mm x 150 mm) multi-mode column using an eluent containing 90 mM ammonium sulfate and 10 mM ammonium nitrate, adjusted to pH 3.5. At a flow of 0.3 mL min(-1) the separation of both Cr species was possible within 8 min. Further the octopole reaction system of the inductively coupled plasma mass spectrometer was systematically studied and optimised to reduce the influence of polyatomic interferences. The major advantage of the developed method compared to published methods is that a derivatisation of the Cr(III) species--an invasion in the speciation--is not required. With the used multi-mode column both chromium species are retained. Furthermore the pH of the mobile phase (pH 3.5) prevents reduction of Cr(VI) as well as precipitation of Cr(III) during the analysis. A limit of determination of approximately 0.5 microg L(-1) for both chromium species with an injection volume of 25 microL was obtained. The optimised method was successfully applied to the determination of Cr(VI) in cement samples as well as chromium speciation analysis in homeopathic drugs.     

Simultaneous speciation of arsenic,selenium, and chromium: species stability,sample preservation,and analysis of ash and soil leachates

An analytical method using high-performance liquid chromatography separation with inductively coupled plasma mass spectrometry (ICP-MS) detection previously developed for the determination of Cr(III) and Cr(VI) has been adapted to allow the determination of As(III), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI) under the same chromatographic conditions. Using this method, all six inorganic species can be determined in less than 3 min. A dynamic reaction cell (DRC)–ICP-MS system was used to detect the species eluted from the chromatographic column in order to reduce interferences. A variety of reaction cell gases and conditions may be utilized with the DRC–ICP-MS, and final selection of conditions is determined by data quality objectives. Results indicated all starting standards, reagents, and sample vials should be thoroughly tested for contamination. Tests on species stability indicated that refrigeration at 10 °C was preferential to freezing for most species, particularly when all species were present, and that sample solutions and extracts should be analyzed as soon as possible to eliminate species instability and interconversion effects. A variety of environmental and geological samples, including waters and deionized water [leachates] and simulated biological leachates from soils and wildfire ashes have been analyzed using this method. Analytical spikes performed on each sample were used to evaluate data quality. Speciation analyses were conducted on deionized water leachates and simulated lung fluid leachates of ash and soils impacted by wildfires. These results show that, for leachates containing high levels of total Cr, the majority of the chromium was present in the hexavalent Cr(VI) form. In general, total and hexavalent chromium levels for samples taken from burned residential areas were higher than those obtained from non-residential forested areas. Arsenic, when found, was generally in the more oxidized As(V) form. Selenium (IV) and (VI) were present, but typically at low levels.     

Speciation of Chromium in Water Samples by Cloud Point Extraction Combined with Low Temperature Electrothermal Vaporization ICP‐OES

Abstract

A new method based on cloud point extraction (CPE) separation and electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV‐ICP‐OES) detection was proposed for the determination of chromium species. Thenoyltrifluoracetone (TTA) was used as both an extractant for CPE of Cr(III) and a chemical modifier for ETV‐ICP‐OES determination. When the system temperature is higher than the cloud point temperature (CPT) of the selected surfactant, Triton X‐114, the complex of Cr(III) with TTA could enter the surfactant‐rich phase, whereas the Cr(VI) remained in aqueous solutions. Thus, an in situ separation of Cr(III) and Cr(VI) could be realized. The concentrated analyte was introduced into ETV‐ICP‐OES for determination of Cr(III) after proper disposal. Cr(VI) is reduced to Cr(III) prior to determining total Cr, and its assay is based on substracting of Cr(III) from total chromium. The main factors affecting cloud point extraction and the vaporization behavior of the analyte were investigated in detail. Under the optimized conditions, the limit of detection (LOD) for Cr(III) was 0.22 µg/L by preconcentration of a 10 mL sample solution, and the relative standard deviation (RSD) was 3.8% (C_Cr(III)=0.5 µg/mL, n=5). The proposed method was applied to the speciation of chromium in different water samples. In order to verify the accuracy of the method, a certified reference water sample was analyzed, and the results obtained were in good agreement with certified values.     

A novel kinetic determination of dissolved chromium species in natural and industrial waste water

A highly sensitive, selective and simple kinetic method was developed for the determination of dissolved chromium species based on the catalytic effect of Cr(III) and/or Cr(VI) on the oxidation of 2-amino-5-methylphenol (AMP) with H₂O₂. The fixed time and initial rate variants were used for kinetic spectrophotometric measurements by tracing the oxidized product at 400 nm for 10 min after starting the reaction. Boric acid and Tween-40 exerted pronounced activating and micellar sensitizing effects on the studied redox reaction, respectively. The optimum reaction conditions were: 3.0 mmol l⁻¹ AMP, 0.45 mol l⁻¹ H₂O₂, 0.50 mol l⁻¹ boric acid, 4 v/v% Tween-40, 10 mmol l⁻¹ phosphate buffer and pH 6.45 ± 0.02 at 35 °C. Both Cr(III) and Cr(VI) ions exerted the same catalytic effect on the studied reaction. Linear calibration graphs were obtained for the determination of up to 6.0 ng ml⁻¹ Cr with detection limits of 0.054 and 0.10 ng ml⁻¹ Cr; following the fixed time and initial rate methods, respectively. The proposed method was successfully applied to the speciation and determination of trace levels of dissolved Cr(III) and Cr(VI) in natural and effluents of industrial waste water. The total dissolved Cr(III) and Cr(VI) species was determined first. In a second run, Cr(VI) was determined alone after precipitation of Cr(III) ions in presence of Al(OH)₃ collector, where Cr(III) is then determined by difference. Moreover, published catalytic-spectrophotometric methods for chromium determination were reviewed.     

Ultrasonic assisted deep eutectic solvent liquid–liquid microextraction using azadipyrromethene dye as complexing agent for assessment of chromium species in environmental samples by electrothermal atomic absorption spectrometry

A novel type of solvent named deep eutectic solvent (DES) has been considered as a green ionic liquid analogue. A novel method was developed for enrichment and speciation of chromium ion from water and food samples based on deep eutectic solvent and ultrasonic extraction. The procedure for this method was comprised of Cr(III) complex formation with a hydrophobic complexing agent (Z)‐N‐(3,5‐diphenyl‐1H‐pyrrol‐2‐yl)‐3,5‐diphenyl‐2H‐pyrrol‐2‐imine (azadipyrromethene dye). Metal complex was entrapped in a deep eutectic solvent as an extracting solvent. While Cr(III) recovery was quantitative, the recovery of Cr(VI) was found 5%. After reduction of Cr(VI) to Cr(III), the method was applied for determination of total chromium(III) ion. The amount of Cr(VI) was calculated as subtracting of Cr(III) from total chromium ion. Various analytical parameters were optimized. The certified reference materials were analyzed and standard addition method also carried out to real samples to check the accuracy of the developed method. Preconcentration factor was found to be 50. The limit of detection of chromium(III) was found to be 4.3 ng l^‐1. The precision of developed method as the relative standard deviation (RSD) was found as 3.5 %. The developed method was applied successfully for the speciation of chromium ions in water and food samples.     

Separation of chromium (III) and chromium (VI) by capillary electrophoresis using 2,6-pyridinedicarboxylic acid as a pre-column complexation agent

A simple method was developed for the simultaneous determination of Cr(III) and Cr(VI) by capillary zone electrophoresis (CZE), where Cr(III) was chelated with ligands to form anionic complexes. Nitrilotriacetic acid, N-2-hydroxyethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and 2,6-pyridinedicarboxylic acid (PDCA) were investigated as Cr(III) complexing ligands. Of all the ligands studied, 2,6-PDCA with Cr(III) gave the largest UV response and high selectivity for Cr(III). In addition, the condition for pre-column derivatization, including pH, concentration ratio [Cr(III)/2,6-PDCA] and the stability of Cr(III) complexes were also examined. The separation of anionic forms of Cr(III) and Cr(VI) was achieved using co-CZE with UV detection at 185 nm. The electrolyte contained 30 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide, 0.1 mM 2,6-PDCA and 15% (v/v) acetonitrile at pH 6.4. The detection limits were 2 microM for Cr(III) and 3 microM for Cr(VI) and linear plots were obtained in a concentration range of 5-200 microM. The utility of the method was demonstrated for the determination of Cr(III) and Cr(VI) in contaminated soils.     

Speciation of Cr(III) and Cr(VI) in Environmental Samples after Solid Phase Extraction on Amberlite XAD–2000

A method for speciation of Cr(III) and Cr(VI) in real samples has been developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its pyrrolidinedithiocarbamate (APDC) complex by using a column containing Amberlite XAD–2000 resin and determined by FAAS. Total chromium has also been determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with KMnO₄. Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of pH, flow‐rate, adsorption and batch capacity and effect of various metal cations and salt anions on the sorption onto the resin were investigated. The adsorption is quantitative in the pH range of 1.5–2.5, and Cr(VI) ion was desorbed by using H₂SO₄ in acetone. The recovery of Cr(VI) was 97 ± 4 at a 95% confidence level. The highest preconcentration factor was 80 for a 200 mL sample volume. The adsorption and batch capacity of sorbent were 7.4 and 8.0 mg g^?1 Cr(VI), respectively, and loading half time was 5.0 min. The detection limit of Cr(VI) is 0.6 μg/L. The procedure has been applied to the determination and speciation of chromium in stream water, tap water, mineral spring water and spring water. Also, the proposed method was applied to total chromium preconcentration in microwave digested moss and rock samples with satisfactory results. The developed method was validated with CRM‐TMDW‐500 (Certified Reference Material Trace Metals in Drinking Water) and BCR‐CRM 144R s (Certified Reference Material Sewage Sludge, Domestic Origin) and the results obtained were in good agreement with the certified values. The relative standard deviations were below 6%.     

Simultaneous determination of arsenic species and chromium(VI) by high-performance liquid chromatography-inductively coupled plasma-mass spectrometry

The simultaneous determination of As(III), As(V), monomethylarsenic acid (MMA), dimethylarsinic acid (DMA) and Cr(VI) in fresh water has been carried out by coupling an anion-exchange column to an inductively coupled plasma-mass spectrometer. Optimisation of chromatographic conditions led to baseline separation of signals from the five species in approximately 9 min using gradient elution. Detection limits were 0.02-0.05 microg As l(-1) and 5.5 microg Cr l(-1). Repeatability was 2-3% for arsenic species and higher, i.e., 8%, for Cr(VI) due to the higher background for this species. Arsenic species and hexavalent chromium stability in surface water samples was evaluated, and storage conditions were set to 1 day at 4 degrees C in polyethylene flasks (without acidification) in order to avoid As(III)-As(V) conversions. The method was applied to the analysis of surface water.     

The effect of Cr(III)-organic complexes on the determination of inorganic chromium species in groundwater by ammonium pyrrolidinedithiocarbamate–methylisobutylketone extraction procedure

Groundwater samples collected from a tannery contaminated area were analyzed for chromium species with the objective of investigating the interference of Cr(III)-organic complexes in the determination of Cr(VI) using APDC–MIBK extraction procedure. The contribution of Cr(III), Cr(VI) and Cr(III)-organic complexes towards total chromium ranged between 2 and 61%, 27 and 86%, and, 6 and 23%, respectively. The Cr(III)-organic complexes were not extractable by APDC–MIBK, however, HNO₃ digestion released the organic bound Cr(III). Interference of organic bound Cr(III) in Cr(VI) determination due to MIBK soluble Cr(III) was not observed. Significant difference between total dissolved chromium determined after appropriate digestion procedure, and the sum of dissolved Cr(III) and Cr(VI) determined indicates the presence of the Cr(III)-organic complexes. MIBK extraction of samples without APDC is an useful way to check the extractability of organic bound Cr(III). The presence of soluble Cr(III)-organic complexes thus add complexity to chromium speciation analysis by APDC–MIBK procedure.     

Speciated isotope dilution analysis of Cr(III) and Cr(VI) in water by ICP-DRC-MS

An isotope dilution method has been developed for the speciation analysis of chromium in natural waters which accounts for species interconversions without the requirement of a separation instrument connected to the mass spectrometer. The method involves (i) in-situ spiking of the sample with isotopically enriched chromium species; (ii) separation of chromium species by precipitation with iron hydroxide; (iii) careful measurement of isotope ratios using an inductively coupled plasma mass spectrometer (ICP-MS) with a dynamic reaction cell (DRC) to remove isobaric polyatomic interferences. The method detection limits are 0.4 μg L⁻¹ for Cr(III) and 0.04 μg L⁻¹ for Cr(VI). The method is demonstrated for the speciation of Cr(III) and Cr(VI) in local nullah and synthetically spiked water samples. The percentage of conversion from Cr(III) to Cr(VI) increased from 5.9% to 9.3% with increase of the concentration of Cr(VI) and Cr(III) from 1 to 100 μg L⁻¹, while the reverse conversion from Cr(VI) to Cr(III) was observed within a range between 0.9% and 1.9%. The equilibrium constant for the conversion was found to be independent of the initial concentrations of Cr(III) and Cr(VI) and in the range of 1.0 (at pH 3) to 1.8 (at pH 10). The precision of the method is better than that of the DPC method for Cr(VI) analysis, with the added bonuses of freedom from interferences and simultaneous Cr(III) determination.     

Speciation Analysis of Cr(III) and Cr(VI) after Solid Phase Extraction Using Modified Magnetite Nanoparticles

A new solid phase extraction (SPE) method has been developed for the speciation of Cr(III) and Cr(VI). This method is based on the adsorption of Cr(VI) on modified alumina‐coated magnetite nanoparticles (ACMNPs). Total chromium in different samples was determined as Cr(VI) after oxidation of Cr(III) to Cr(VI) using H₂O₂. The chromium concentration has been determined by flame atomic absorption spectrometric (FAAS) technique and amount of Cr(III) was calculated by substracting the concentration of Cr(VI) from total chromium concentration. The effect of parameters such as pH, amount of adsorbent, contact time, sample volume, eluent type, H₂O₂ concentration and cetyltrimethylammonium bromide (CTAB) concentration as modifier on the quantitative recovery of Cr(VI) were investigated. Under the optimal experimental conditions, the preconcentration factor, detection limit, linear range and relative standard deviation (RSD) of Cr(VI) were 140 (for 350 mL of sample solution), 0.083 ng mL^?1, 0.1‐10.0 ng mL^?1 and 4.6% (for 5.0 ng mL^?1, n = 7), respectively. This method avoided the time‐consuming column‐passing process of loading large volume samples in traditional SPE through the rapid isolation of CTAB@ACMNPs with an adscititious magnet. The proposed method was successfully applied to the determination and speciation of chromium in different water and wastewater samples and suitable recoveries were obtained.     

Simultaneous determination of hexavalent and total chromium in water and plating baths by spectrophotometry

A new spectrophotometric determination method of hexavalent chromium in waste water and plating baths is described based on the oxidation of beryllon III by chromium(VI) in 0.02M sulphuric acid medium. The decrease in the absorbance of beryllon III was measured at 482 nm with an apparent molar absorptivity of 5.15 x 10(4)1.mole(-1).cm(-1). Beer's law was obeyed for chromium(VI) over the range 0-25 mug/25 ml. After the oxidation of Cr(III) to Cr(VI) by ammonium persulphate, total chromium can be determined. Therefore, chromium(III) can be calculated by subtracting chromium(VI) from total chromium. The detection limit is 0.015 and 0.020 mug/25 ml for chromium(VI) and total chromium, respectively. A sensitive spectrophotometric method for trace Cr(III) and Cr(VI) in waste water and plating baths was developed with good precision and accuracy. The reaction is also discussed.     

Speciation of V, Cr and Fe by capillary electrophoresis-bandpass reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis-dynamic reaction cell inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the speciation of iron(III/II), vanadium(V/IV) and chromium(VI/III) is described. Two different CE migration modes were employed for separating the six metal ions using pre-capillary complexation. One is counter-electroosmotic mode in which iron(III/II) and vanadium(V/IV) ions were well separated using a 60 cm x 75 microm i.d. fused silica capillary. The voltage was set at +22 kV and a 15 mmol l(-1) tris(hydroxymethyl)aminomethane (Tris) buffer (pH 8.75) containing 0.5 mmol l(-1) ethylenediaminetetraacetic acid (EDTA) and 0.5 mmol l(-1) ortho-phenanthroline (phen) was used as the electrophoretic buffer. The other is co-electroosmotic mode in which chromium(VI/III) ions were well separated while the applied voltage was set at -22 kV and a 10 mmol l(-1) ammonium citrate buffer (pH 7.7) containing 0.5 mmol l(-1) diethylenetriaminepentaacetic acid (DTPA) and 0.01% polybrene was used as the electrophoretic buffer. The mass spectra were measured at m/z 51, 52 and 56 for V. Cr and Fe, respectively. The interfering polyatomic ions of 35Cl16O+, 40Ar12C+ and 40Ar16O+ on 51V+, 52Cr+ and 56Fe+ determination were reduced in intensity significantly by using NH3 as the reaction cell gas in the DRC. The detection limits were in the range of 0.1-0.5, 0.4-1.3 and 1.2-1.7 ng ml(-1) for V, Cr and Fe, respectively. Applications of the method for the speciation of V, Cr and Fe in wastewater were demonstrated. The recoveries were in the range of 92-120% for various species.     

On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry

On-line preconcentration system for the selective, sensitive and simultaneous determination of chromium species was investigated. Dual mini-columns containing chelating resin were utilized for the speciation and preconcentration of Cr(III) and Cr(VI) in water samples. In this system, Cr(III) was collected on first column packed with iminodiacetate resin. Cr(VI) in the effluent from the first column was reduced to Cr(III), which was collected on the second column packed with iminodiacetate resin. Hydroxyammonium chloride was examined as a potential reducing agent for Cr(VI) to Cr(III).The effects of pH, sample flow rate, column length, and interfering ions on the recoveries of Cr(III) were carefully studied. Five millilitres of a sample solution was introduced into the system. The collected species were then sequentially washed by 1 M ammonium acetate, eluted by 2 M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15 μg l⁻¹, respectively. The total analysis time was about 9.4 min.The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results.     

Preconcentration and Determination of Chromium Species Using Octadecyl Silica Membrane Disks and Flame Atomic Absorption Spectrometry

A novel and selective method for the fast determination of trace amounts of chromium species in water samples has been developed. The procedure is based on the selective formation of chromium diethyldithiocarbamate complexes at different pH in the presence of Mn(II) as an enhancement agent of chromium signals followed by elution with organic eluents and determination by atomic flame absorption spectrometry. The maximum capacity of the employed disks was found to be (396±3) µg and (376±2) µg for Cr(III) and Cr(VI), respectively. The detection limit of the proposed method is 49 and 43 ng·L^?1 for Cr(III) and Cr(VI), respectively. The proposed method was successfully applied for determination of chromium species Cr(III) and Cr(VI) in different water samples.     

Speciation Analysis of Chromium by Adsorptive Stripping Voltammetry in Tap and River Water Samples

An adsorptive stripping voltammetric method for speciation analysis of chromium in natural water samples has been developed. Ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) were used as complexing agents for Cr(III) present in the sample and formed as products of Cr(VI) reduction, respectively. Under optimum experimental conditions linear relations in the range from 1×10^?6 to 3×10^?5 mol L^?1 without accumulation and from 1×10^?9 to 1×10^?7 at 30 s accumulation time were obtained for Cr(III) and Cr(VI), respectively. For samples in which Cr(III) concentration is higher than 1×10^?6 mol L^?1 the Cr(III) and Cr(VI) were determined simultaneously in one voltammetric cell. For samples in which Cr(III) concentration is below 1×10^?6 mol L^?1 only Cr(VI) was selectively determined in the presence of Cr(III), which did not influence the Cr(VI) signal. The determination of Cr(III) and Cr(VI) was successful with the application of the proposed procedure in the presence of common foreign ions. The presented method was applied for the speciation of chromium in spiked tap and river water samples with satisfactory results.     

Tea-industry waste activated carbon, as a novel adsorbent, for separation, preconcentration and speciation of chromium

Activated carbon was produced from tea-industry wastes (TIWAC) and employed as a low cost and effective solid phase material for the separation, preconcentration and speciation of chromium species without using a complexing agent, prior to determination by flame atomic absorption spectrometry (FAAS). The characterization of TIWAC was performed by utilizing several techniques such as Fourier Transform Infrared (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), and elemental analysis. The adsorption experiments were conducted in a batch adsorption technique. Under the experimental conditions, Cr(VI) adsorption amount was nearly equal to zero, however the adsorption percentage of Cr(III) was in the range of 95–100%. Therefore total chromium was determined after the reduction of Cr(VI) to Cr(III) and Cr(VI) was calculated by subtracting Cr(III) concentration from total chromium concentration. The suitable conditions for adsorption and speciation processes were evaluated in terms of pH, eluent type and volume, TIWAC concentration, adsorption and desorption contact time, etc. Adsorption capacity of TIWAC was found to be 61.0 mg g⁻¹. The detection limit for Cr(III) was found to be 0.27 μg L⁻¹ and the preconcentration factor was 50 for 200 mL of sample volume. The procedure was applied to the determination and speciation of chromium in stream, tap and sea water. Also, the proposed method was applied to total chromium preconcentration in microwave digested tobacco and dried eggplant samples with satisfactory results. The method was validated by analyzing certified reference materials (CRM-TMDW-500 Drinking Water and CRM-SA-C Sandy Soil C) and the results were in good agreement with the certified values.     

Simultaneous Determination of Chromium Species in Water and Plant Samples at Trace Levels by Ion Chromatography–Inductively Coupled Plasma-Mass Spectrometry

Ion chromatography–inductively coupled plasma-mass spectrometry (IC–ICP-MS) was used for the identification and quantification of chromium species. Chromium(III) and chromium(VI) were separated and determined by IC–ICP-MS. The separation was achieved using an anion exchange column with 0.55?M HNO₃ as mobile phase. It was a particular goal of this work to exclusively use nitric acid for elution in order to reduce interferences in the ICP-MS system. Analytical figures of merit were calculated under the optimum conditions by developing calibration plots in a concentration range of 0.50–250?µg/L for both species. The detection limits for Cr(III) and Cr(VI) were 0.09 and 0.03?µg/L, respectively. Spiked recovery tests were used to evaluate the applicability of the analytical method in environmental samples, and the recoveries ranged between 97 and 103% for both analytes. The accuracy of the method for total chromium content was validated through the analysis of a spring water-certified reference material (UME 1201), and the obtained results were in good agreement with the certified value. Lettuce seedlings were cultivated to evaluate the intake levels of these species. In addition, the bioaccessibility of Cr(III) and Cr(VI) from the lettuce seedlings in simulated gastric and intestinal fluids media was examined.     

Speciation of Cr(III) and Cr(VI) using solid phase extraction and determination of total As inductively coupled plasma atomic emission spectrometry

An inductively coupled plasma atomic emission spectrometric (ICP-AES) method was developed for speciation and simultaneous determination of Cr and As, since these two analytes are commonly determined in various water samples in order to assess their toxicity. The objective of this research was to study the speciation of Cr(III), Cr(VI) in the presence of As(III) and/or As(V) using solid phase extraction (SPE) and ICP-AES. For these measurements, four spectral lines were used for each analyte with the purpose of selecting the most appropriate for each element. Finally with the use for first time of a cation-exchange column filled with benzosulfonic acid and elution with HCl, the speciation in solutions which contained [Cr(III)?+?Cr(VI)?+?As(V)] and [Cr(III)?+?Cr(VI)?+?As(III)] was examined. It was demonstrated that the separation of the two chromium species is almost quantitative and the simultaneous determination of chromium species and total arsenic analytes is possible, with very good performance characteristics. The estimated limits of detection for Cr(III), Cr(VI), As(III) and/or As(V) were 0.9?µg?L^?1, 1.1 µg?L^?1, 4.7 µg?L^?1 and 4.5 µg?L^?1 respectively, the calculated relative standard deviations (RSDs) were 3.8%, 4.1%, 5.2% and 5.1% respectively, and finally the accuracy of the methods was estimated using a certified aqueous reference material and found to be 5.6% and 4.8% for Cr(III) and Cr(VI) respectively. The method was applied to the routine analysis of various water samples.     

Speciation of chromium in wastewater and sludge by extraction with liquid anion exchanger Amberlite LA-2 and electrothermal atomic absorption spectrometry

A simple, integrated method for the speciation of chromium in wastewater and sewage sludge was developed, utilising liquid anion exchange by Amberlite LA-2 (LAES) and final determination by electrothermal atomic absorption spectrometry (ETAAS). Samples were filtered through a 0.45 μm membrane filter and chromium species were determined in filtered water samples and in sludge on the filters. In the former case (filtrate), total Cr was determined directly by ETAAS, while for the determination of Cr(VI) the filtrate was buffered to pH 6.4, extracted with LAES and Cr(VI) was determined in the organic extract. Cr(III) was determined by the difference. In the latter case (filter), the filters were leached with an alkaline buffer solution (pH 12.7) and the supernatant was subjected to the same extraction procedure. For the determination of total leachable Cr, the filters were subjected to acid leaching with dilute HNO₃ (pH 1) and the supernatant was subjected to ETAAS, after appropriate dilution with water. Then, Cr(III) was determined by the difference. The limits of detection (LOD) were 0.39 and 0.45 μg l⁻¹ for total Cr and Cr(VI), respectively, in the dissolved phase and 2.10 and 0.87 ng g⁻¹ for total Cr and Cr(VI) in the suspended solids. The recoveries of total Cr and Cr(VI) in filtrated wastewater samples and filters were quantitative, ranged from 93 to 106%. The effect of time and temperature of sonication and suspended solids concentration on total Cr and Cr(VI) recovery was studied. No significant difference in recoveries was obtained for sonication temperatures between 30 and 70 °C. However, sonication time equal to or higher than 30 min and concentration of suspended solids equal to or less than 30 mg significantly improved Cr recovery. The ETAAS program for the determination of Cr(VI) in Amberlite/MIBK extract was carefully optimised in the absence of a chemical modifier to avoid memory effects. The developed analytical method was applied for the determination of chromium species in wastewater and suspended solids of a municipal and a lab-scale wastewater treatment plant.