Chromium speciation by a surfactant-coated alumina microcolumn using electrothermal atomic absorption spectrometry

A simple and convenient method has been developed for the speciation of chromium(III) and chromium(VI) in aqueous solutions using a sodium dodecyl sulphate coated alumina micro-column (1.5 cm x 5 mm i.d.) and graphite furnace-atomic absorption spectrometry (GF-AAS). Under the optimized conditions (pH 0.6, adjusted with hydrochloric acid; flow rate, 1 ml min(-1)) chromium(VI) is retained on the column and chromium(III) is collected and determined by GF-AAS. Total chromium is directly determined by GF-AAS and chromium(VI) is calculated by difference. The relative standard deviations (10 replicate analyses) at the 20 mug l(-1) level for chromium(III) and chromium(VI) and at the 40 mug l(-1) level for total chromium were 1.4%, 3.6% and 1.8%, and the corresponding limits of detection (based on 3sigma) were 0.57 mug ml(-1), 0.61 mug ml(-1) and 0.35 mug l(-1) respectively. No large interference effects have been observed from other investigated species and the method has been successfully applied to a range of water samples.     

Determination of trace metals and speciation of chromium ions in atmospheric precipitation by ICP-AES and GFAAS

Sampling and analytical techniques used for determining trace metal concentrations in atmospheric precipitation waters collected in Hungary are presented. The results of the analyses are briefly discussed and special attention is devoted to chromium speciation. For the preconcentration of the trace metals a chelating cellulose, iminodiacetic acid ethylcellulose (IDAEC) microcolumn was used in a flow-injected system. Cd, Co, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn were determined by ICP-AES. In precipitation water the concentrations of the trace elements were in the 0.1-50 mug/l. range. The two forms of chromium, Cr(III) and Cr(VI) were separated using IDAEC and the anion exchanger diethylamine ethylcellulose, respectively. Cr was determined by GFAAS. In atmospheric precipitation the concentration of Cr(III) was in the range of 0.1-0.4 mug/l. while that of Cr(VI) in the range of 0.04-0.1 mug/l.     

Chromium speciation using activated alumina microcolumns and sequential injection analysis-flame atomic absorption spectrometry

A new procedure has been developed for chromium speciation in water by sequential injection analysis and flame atomic absorption spectrometry. The method involves the online retention of Cr(VI) anionic species and Cr(III) cationic species on alumina microcolumns, prepared by packing activated alumina in polytetrafluoroethylene tubes, followed by selective elution of Cr(VI) with 2 mol l⁻¹ NH₄OH and of Cr(III) with 0.2 mol l⁻¹ HNO₃. Studies were carried out on the effect of retention and elution conditions for both Cr species. The limit of detection values, established as the concentration corresponding to three times the standard deviation of blank measurements divided by the slope of the calibration line, achieved were 42 μg l⁻¹ for Cr(VI) and 81 μg l⁻¹ for Cr(III). The relative standard deviation of three independent determination of natural spiked samples were lower than 10% for concentration levels between 0.5 and 2 mg l⁻¹ of Cr. The developed procedure was applied to the analysis of two effluent sewage waters, and results obtained compared well with those obtained by a batch procedure. Recovery studies on natural spiked samples provided results between 93 and 103% for Cr(VI) and from 100 to 106% for Cr(III) for samples spiked with single species. For samples spiked with both Cr(VI) and Cr(III), the average recoveries varied from 86 to 101% for Cr(VI) and from 91 to 117% for Cr(III).     

Speciation of Cr(III) and Cr(VI) by Means of Melamine-Urea-Formaldehyde Resin and FAAS

 A method is described for the quantitative preconcentration and separation of trace chromium in water by adsorption on melamine-urea-formaldehyde resin. Cr(VI) is enriched from aqueous solutions on the resin. After elution the Cr(VI) is determined by FAAS. The capacity of the resin is maximal at ∼ pH 2. Total chromium can be determined by the method after oxidation of Cr(III) to Cr(VI) by hydrogen peroxide. The relative standard deviations (10 replicate analyses) for 10 mg/L levels of Cr(VI), Cr(III) and total chromium were 1.5, 3.5 and 2.8% respectively. The procedure has been applied to the determination and speciation of chromium in lake water, tap water and chromium-plating baths.     

Chromium(III)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection

A new chromium(III)-imprinted 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS)-functionalized silica gel sorbent was synthesized by a surface imprinting technique and was employed as a selective solid-phase extraction material for speciation analysis of chromium in environmental water samples prior to its determination by inductively coupled plasma mass spectrometry (ICP-MS). The prepared Cr(III)-imprinted silica gel shows the selectivity coefficient of more than 700 for Cr(III) in the presence of Mn(II). The static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Cr(III) were 30.5 mg g(-1) and 13.4 mg g(-1). It was also found that Cr(VI) could be adsorbed at low pH by the prepared imprinted silica gel, and this finding makes it feasible to enrich and determine Cr(VI) at low pH without adding reducing reagents. The imprinted silica gel sorbent offered a fast kinetics for the adsorption and desorption of both chromium species. Under the optimized conditions, the detection limits of 4.43 pg mL(-1) and 8.30 pg mL(-1) with the relative standard deviations (R.S.D.s) of 4.44% and 4.41% (C=0.5 ng mL(-1), n=7) for Cr(III) and Cr(VI) were obtained, respectively. The proposed method was successfully applied to the speciation of trace chromium in environmental water samples. To validate the proposed method, two certified reference materials were analyzed and the determined values were in a good agreement with the certified values. The developed method is rapid, selective, sensitive and applicable for the speciation of trace chromium in environmental water samples.     

Anion exchange separation of chromium and molybdenum from iron,vanadium, uranium and other elements in malonic acid solution

Summary Anion-exchange behaviour of chromium (III) and molybdenum (VI) was studied in malonate media. They form anionic complexes with malonic acid at pH 5.6. Various eluants, such as mineral acids and their salts were tested and a selectivity scale evolved. Cr and Mo were separated from Tl(I), alkali and alkaline earth elements by selective sorption and from Co(II), Ni(II), Mn(II), Zn(II) and Cd(II) by selective washing with water. They were separated from many other elements by selective elution. The sequential separation of Fe(III) V(IV), Cr(III), Mo(VI) and U(VI) was significant.     

Simultaneous determination of Cr(III)-EDTA and Cr(VI) by ion interaction chromatography using a C18 column

The simultaneous determination of Cr(III) and Cr(VI) by ion interaction chromatography has been investigated. The mobile phase consisted of a 5 mM octylammonium orthophosphate at pH 4.0 with 35% (v/v) MeOH. The Nucleosil-100, C18 (5 microm, 250 x 4.6 mm) was used as the separating column and the component was detected at 200 nm. The separation of Cr(III) and Cr(VI) was based on anionic interaction. Since the Cr(III) did not exist as an anionic form like the Cr(VI) (Cr2O7(2-)) presented at the optimum condition, Cr(II) was firstly reacted with EDTA (1:40 mole ratio) to form the anionic complex prior to injecting into the chromatographic system. The characteristics of the method for separation of Cr(III)-EDTA and Cr(VI) were satisfactory. The wide linear range (0.3-50.0 mg l(-1)) was achieved. The repeatabilities (%R.S.D.) calculated from peak areas were 0.49% and 0.14%, detection limit (signal to noise ratio of 3) of 0.02 mg l(-1) and 0.3 mg l(-1) were obtained and the average of percent recoveries were found to be 98.5% and 99.6% for Cr(III) and Cr(VI), respectively.     

Determination of chromium(III) and total chromium in natural waters using a surface ion-imprinted silica gel as selective adsorbent

A sensitive and selective method has been developed to determine Cr(III) and total Cr in natural water samples by ICP-AES with a Cr(III)-imprinted aminopropyl-functionalised silica gel adsorbent. The Cr(III)-imprinted and non-imprinted adsorbent were prepared by an easy one-step reaction with a surface imprinting technique. Their maximum static adsorption capacities for Cr(III) were 11.12 mg g^?1 and 3.81 mg g^?1, respectively. The relative selectivity factors (α _r) for Cr(III)/Co(II), Cr(III)/Au(III), Cr(III)/Ni(II), Cr(III)/Cu(II), Cr(III)/Zn(II), and Cr(III)/Cr(VI), were 377, 21.4, 15.4, 27.7, 26.4, and 31.9, respectively. Under the optimal conditions, Cr(III) can be absorbed quantitatively, but Cr(VI) was not retained. Total chromium was obtained after reducing Cr(VI) to Cr(III) with hydroxyammonium chloride. The detection limit (3σ) for Cr(III) was 0.11 ng mL^?1. The relative standard deviation was 1.2%. The proposed method has been validated by analysing two certified reference materials and successfully applied to the determination and speciation of chromium in natural water samples with satisfactory results.     

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 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.     

Cloud point extraction for high-performance liquid chromatographic speciation of Cr(III) and Cr(VI) in aqueous solutions

Cloud point extraction (CPE) was applied as a preconcentration step for HPLC speciation of chromium in aqueous solutions. Simultaneous preconcentration of Cr(III) and Cr(VI) in aqueous solutions was achieved by CPE with diethyldithiocarbamate (DDTC) as the chelating agent and Triton X-114 as the extractant. Baseline separation of the DDTC chelates of Cr(III) and Cr(VI) was realized on a RP-C18 column with the use of a mixture of methanol-water-acetonitrile (65:21:14, v/v) buffered with 0.05 M NaAc-HAc solution (pH 3.6) as the mobile phase at a flow rate of 1.0 ml min(-1). The precision (R.S.D.) for eight replicate injections of a mixture of 100 microg l(-1) of Cr(III) and Cr(VI) were 0.6 and 0.5% for the retention time, 4.1 and 4.6% for the peak area measurement, respectively. The concentration factor, which is defined as the concentration ratio of the analyte in the final diluted surfactant-rich extract ready for HPLC separation and in the initial solution, was 65 for Cr(III) and 19 for Cr(VI). The linear concentration range was from 50 to 1000 microg l(-1) for Cr(III) and 50-2000 microg l(-1) for Cr(VI). The detection limits of Cr(III) and Cr(VI) were 3.4 and 5.2 microg l(-1), respectively. The developed method was applied to the speciation of Cr(III) and Cr(VI) in snow water, river water, seawater and wastewater samples.     

Chromium speciation by surfactant assisted solid-phase extraction and flame atomic absorption spectrometric detection

A new procedure has been developed for chromium speciation in aqueous solution by the use of micellar, ion-association, solid-phase extraction techniques (SPE) followed by flame atomic absorption spectrometry. The method was based on the use of C-18 bonded phase silica SPE disks for retention of ion-associated Cr(VI) with cetyl trimethyl ammonium bromide (CTAB), elution of the retained species and subsequent detection by flame atomic absorption spectrometry (FAAS). Cr(III) was oxidized by potassium persulfate to Cr(VI), then the total chromium was retained on the disk and determined by FAAS. The amount of Cr(III) was calculated by the difference between the total and Cr(VI) values. The calculated limit of detections (LOD) (based on 3sigma) are 15 microg L(-1) and 20 microg L(-1) for Cr(VI) and Cr(III) respectively. No considerable interferences have been observed from other investigated anions and cations and the method has been successfully applied to water samples taken from the Karoon River in Khuzestan province.     

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.     

Speciation of chromium in seawater by ICP-AES with dual mini-columns containing chelating resin.

A method for the preconcentration and speciation of chromium in seawater was developed. On-line preconcentration and determination were carried out by using inductively coupled plasma atomic emission spectrometry (ICP-AES) with dual mini-columns containing a chelating resin. In this system, Cr(III) was collected on the first column. The effluent containing residual chromium from the first column was collected on the second column after passing through a reduction-switching unit, in which the reducing agent was introduced, or not, for the reduction of Cr(VI) to Cr(lII). Cr(VI) was determined as the difference between the concentration of pre-reduced Cr(VI) and Cr(III) in the effluent from the first column. The detection limits for Cr(III) and Cr(VI) were 0.04 and 0.09 microg l(-1), respectively.     

Speciation of Cr(III) and Cr(VI) in environmental samples by using coprecipitation with praseodymium(III) hydroxide and determination by flame atomic absorption spectrometry

A speciation procedure has been established for the flame atomic absorption spectrometric determination of Cr(III) and Cr(VI) based on coprecipitation of Cr(III) by using praseodymium(III) hydroxide (Pr(OH)₃) precipitate. In the presented system, Cr(III) was quantitatively (>95%) recovered at the pH range of 10.0?C12.0 on Pr(III) hydroxide, while the recoveries of Cr(VI) were below 10%. The method was applied to the determination of the total chromium after reduction of Cr(VI) to Cr(III) by using hydroxylamine hydrochloride. The concentration of Cr(VI) is calculated by difference of total chromium and Cr(III) levels. The analytical parameters including pH of the aqueous medium, amount of Pr(III), centrifugation speed, sample volume were optimized. The influences of matrix ions were also investigated. The method was validated by the analysis of TMDA 70 fortified lake water certified reference material. The method was applied to the speciation of chromium in water samples.     

Sequential injection wetting film extraction applied to the spectrophotometric determination of chromium(VI) and chromium(III) in water

The spectrophotometric determination of Cr(VI) and Cr(III) via sequential injection was used to demonstrate the sensitivity enhancement provided by a newly developed wetting film extraction system. The reaction product of Cr(VI) with 1,5-diphenylcarbazide was ion-paired with perchlorate and extracted into an organic wetting film consisting of octanol and 4-methyl-2-pentanone on the inner wall of a Teflon tube. The wetting film, with the extracted analyte, was then eluted with 100 mul acetonitrile and the analyte determined spectrophotometrically at 546 nm. Important optimized parameters were the selection of wetting film and elution solvents, the flow rate, the length and diameter of the extraction coil and the conditions for the formation of the ion paired chelate. Cr(III) was previously oxidized to Cr(VI) and calculated as the difference between total Cr and Cr(VI). An enrichment factor of 25 and a detection limit of 2.0 mug l(-1) Cr(VI) were achieved with a sampling frequency of 17 h(-1). The calibration curve was linear up to 100 mug l(-1) Cr(VI) (r = 0.999). The relative standard deviations were 2.8 and 2.0% at the 25 and 100 mug l(-1) levels.     

Separation of Cr(III) and Cr(VI) using melamine-formaldehyde resin and determination of both species in water by FAAS

A method is described for the determination of Cr(VI) and total chromium by FAAS. Cr(VI) is separated from Cr(III) by adsorption on melamine-formaldehyde resin. After elution of Cr(VI) with 0.1 mol/l NaAc solution, it is analysed by FAAS. Total chromium is determined by FAAS after conversion of Cr(III) to Cr(VI) by oxidation with hydrogen peroxide, total Cr(VI) is concentrated as above. If the total concentration of chromium is sufficient, the determination can be directly made by FAAS. Cr(III) can then be calculated by subtracting Cr(VI) from the total Cr. This method was successfully applied to the determination of chromium in lake water.     

Ion-pair chromatographic determination of chromium(VI)

Ion-pair chromatography (IPC) with conductometric detection was investigated as a precise and selective analytical method for the determination of chromium in electro-plating solutions and waste waters. Chromatographic parameters were optimized for separation of Cr(VI) and SO(2-)(4). The analytical column (100 x 6 mm) was packed with 10 mum silasorb C(18) (Czechoslovakia). Tetrabutylammonium butyrate (TBAB), at pH 7.0 in acetonitrile-water (18:82 v/v) mixture, was used as the eluent. Two samples of solution are taken for the analysis. In the first of them the amount of Cr(VI) is determined, in the second one Cr(III) is oxidized to Cr(VI) with H(2)O(2) in alkaline medium and the total amount of Cr is determined. From the difference of the two obtained results the concentration of Cr(III) is calculated. The detection limit of Cr(VI) is 0.1 mug/ml and the relative standard deviation (at the 1.0 mug/ml) is 4.0%. The IPC results for chromium agreed closely with these obtained by spectrophotometry.     

Enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide using internal standard and derivative spectrophotometry

In the present work, erioglaucine A was applied as internal standard to enhanced spectrophotometric determination of chromium (VI) with diphenylcarbazide. The following procedure was used: (1) addition of internal standard and formation of ion pairs of Cr (VI) with benzyltributylammonium bromide (BTAB) (sample volume 100 ml), (2) extraction to 10 ml of methylene chloride, (3) evaporation in nitrogen stream, and (4) redissolution in a micro-volume with addition of diphenylcarbazide for color development (final volume 200 mul). The preconcentration factor achieved was about 400 and it was shown that, using internal standard, the analytical errors due to sample treatment were reduced. The analytical signals for chromium and internal standard were obtained at 591.30 and 653.50 nm from first derivative spectra, normalized against (1)D(653.50nm). The analytical characteristics evaluated were: detection limit = 0.06 mug l(-1), quantification limit = 0.19 mug l(-1), precision for 1 mug l(-1) 14.2%, and for 10 mug l(-1) 3.2%, correlation coefficient of linear regression was 0.9985. The proposed procedure was applied to determination of chromium (VI) in tap water. Total chromium was determined by electrothermal atomic absorption spectrometry, the recovery of hexavalent chromium added was then evaluated and compared with the results of the proposed procedure. In this experiment, good agreement was obtained between results obtained by the two methods.     

Speciation of chromium in water using crosslinked chitosan-bound FeC nanoparticles as solid-phase extractant, and determination by flame atomic absorption spectrometry

Crosslinked chitosan-bound FeC nanoparticles (CCBFeCNP) were prepared, and the adsorptive behavior of Cr(III) and Cr(VI) on CCBFeCNP were assessed. At pH 6.0–10.0, CCBFeCNP is selective towards Cr(III) but hardly selective towards Cr(VI). The retained Cr(III) is subsequently eluted with 0.5 mol L⁻¹ HCl. Total chromium is determined after reduction of Cr(VI) to Cr(III) by ascorbic acid. A new method of flow injection using a micro-column packed with CCBFeCNP as solid phase extractant has been developed for speciation of Cr(III) and Cr(VI) in water samples, followed by flame atomic absorption spectrometry. The effects of pH, sample flow rate and volume, elution solution and interfering ions on the recoveries of Cr(III) were systematically investigated. Under optimum conditions, the adsorption capacity of CCBFeCNP for Cr(III) is 10.5 mg g⁻¹ at pH 7.5. The procedure presented was applied to chromium speciation in water samples, and the results were satisfactory.