Preconcentration and separation of Cr(III) and Cr(VI) using sawdust as a sorbent

A simple, inexpensive method based on solid-phase extraction (SPE) on sawdust from Cedrus deodera has been developed for speciation of Cr(III) and Cr(VI) in environmental water samples. Because different exchange capacities were observed for the two forms of chromium at different pH—Cr(III) was selectively retained at pH 3 to 4 whereas Cr(VI) was retained at pH 1—complete separation of the two forms of chromium is possible. Retained species were eluted with 2.5 mL 0.1 mol L⁻¹ HCl and 0.1 mol L⁻¹ NaOH. Detection limits of 0.05 and 0.04 μg mL⁻¹ were achieved for Cr(III) and Cr(VI), respectively, with enrichment factors of 100 and 80. Recovery was quantitative using 250 mL sample volume for Cr(III) and 200 mL for Cr(VI). Different kinetic and thermodynamic properties that affect sorption of the chromium species on the sawdust were also determined. Metal ion concentration was measured as the Cr(VI)–diphenylcarbazide complex by UV–visible spectroscopy. The method was successfully applied for speciation of chromium in environmental and industrial water samples.     

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.     

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.     

Development of a cloud point extraction and preconcentration method for chromium(III) and total chromium prior to flame atomic absorption spectrometry

A sensitive and selective method has been developed for the determination of chromium in water samples based on using cloud point extraction (CPE) preconcentration and determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Cr(III) ions with Brilliant Cresyl Blue (BCB) in the presence of non-ionic surfactant Triton X-114. Under the optimum conditions, the preconcentration of 50 mL of water sample in the presence of 0.5 g/L Triton X-114 and 1.2 × 10⁻⁵ M BCB permitted the detection of 0.42 μg/L chromium(III). The calibration graph was linear in the range of 1.5–70 μg/L, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Cr(III) in water samples and certified water samples. In addition, the developed CPE-FAAS method was also used for speciation of the inorganic chromium species after reduction of Cr(VI) to Cr(III) using a thiosulphate solution of 120 mg/L in the presence of Hg(II) ion as a stabilizer.     

Flavonol Derivatives for Determination of Cr(III) and W(VI)

 Simple, rapid, sensitive and selective methods for the determination of Cr(III) and W(VI) with flavonol derivatives in the presence of surface-active agents are proposed. In the pH ranges 3.4–4.2 and 1.9–2.5, the molar absorptivities of Cr(III)-morin-emulsifier S (EFA) and W(VI)-morin-polyvinylpyrrolidone (PVP) systems are 1.13×10⁵ and 2.13×10⁴ L mol⁻¹ cm⁻¹ at 435 and 415 nm, respectively. The Cr(III)-quercetin-PVP and W(VI)-quercetin-cetylpyridinium bromide (CPB) systems are formed in the pH ranges 4–4.6 and 2.2–2.8 with molar absorptivities 1.02×10⁵ and 9.02×10⁴ L. mol⁻¹ cm⁻¹ at 441 and 419 nm, respectively. The linear dynamic ranges for the determination of Cr(III) and W(VI) with morin in the presence of EFA and PVP are 0.03–0.46 and 0.71–8.1 μg mL⁻¹, respectively. The corresponding ranges with quercetin are 0.04–0.54 and 0.14–2.1 μg mL⁻¹ of Cr(III) and W(VI), respectively. The r.s.d (n = 10) for the determination of 0.25 and 3.7 μg mL⁻¹ of Cr(III) and W(VI) with morin and their detection limits are 0.88 and 0.99% and 0.016 and 0.63 μg mL⁻¹, respectively. Using quercetin, the r.s.d (n = 10) for 0.22 and 1.2 μg mL⁻¹ of Cr(III) and W(VI) and their detection limits are 0.92 and 0.91% and 0.015 and 0.08 μg mL⁻¹, respectively. The critical evaluation of the proposed methods is performed by statistical analysis of the experimental data. The proposed methods are applied to determine Cr in steel, non-ferrous alloys, wastewater and mud filtrate and to the determination of W in steel. Received March 8, 1999. Revision January 21, 2000.     

Speciation of Cr(VI)/Cr(III) by electrothermal atomisation AAS after electrodeposition on a L'vov platform

Summary The pyrolysed graphite L'vov platform of a tube furnace is considered as an electrode for the electrodeposition and speciation of chromium by electrothermal atomisation atomic absorption spectrometry (ETA-AAS). Firstly, a preliminary study of the Cr(VI)/Cr(III) voltammetric behavior at pH 4.70 on a glassy-carbon electrode is carried out. Secondly, the L'vov platform is used as a cathodic macro-electrode for the selective preconcentration of Cr(VI)/Cr(III) on a mercury film. Speciation of Cr(VI)/Cr(III) is carried out on the basis of the electrolysis potential (E_e): at pH 4.70 and E_e=–0.30 V, only Cr(VI) is reduced to Cr(III) and accumulated as Cr(OH)₃ by adsorption on a mercury film; at E_e=–1.80 V both Cr(VI) and Cr(III) are accumulated forming an amalgam with added mercury(II) ions. Once the film has been formed, the platform is transferred to a graphite tube to atomise the element. The reliability of the method was tested for the speciation of chromium in natural waters and it proves to be highly sensitive thanks to the electroanalytical step. In all samples, the Cr(VI) concentration was less than the detection limit (0.15 ng ml^–1), and the concentration of Cr(III) agrees with those of total chromium. The analytical recovery of Cr(VI) added to water samples [3.50 ng ml^–1 of Cr(VI)] was 105±6.2%.     

Chemiluminescence determination of chromium(III) and total chromium in water samples using the periodate-lucigenin reaction

A new chemiluminescence (CL) method combined with flow injection technique is described for the determination of Cr(III) and total Cr. It is found that a strong CL signal is generated from the reaction of Cr(III), lucigenin and KIO₄ in alkaline condition. The determination of total Cr is performed by pre-reduction of Cr(VI) to Cr(III) by using H₂SO₃. The CL intensity is linearly related to the concentration of Cr in the range 4.0 × 10⁻¹⁰–1.0 × 10⁻⁶ g mL⁻¹. The detection limit (3s _b) is 1 × 10⁻¹⁰ g mL⁻¹ Cr and the relative standard deviation is 1.9% (5.0 × 10⁻⁸ g mL⁻¹ of Cr(III) solution, n = 11). The method was applied to the determination of Cr(III) and total Cr in water samples and compared satisfactorily with the official method.     

Screen-printed sensor for batch and flow injection potentiometric chromium(VI) monitoring

A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite–epoxy composite. The optimal graphite–epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 ± 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO₃ solution at pH 3 as the carrier, a flow rate of 2.5 mL·min⁻¹, and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 × 10⁻⁷ M) and online analysis (9.4 × 10⁻⁷ M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills.     

A catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances

A simple and fast catalytic adsorptive stripping voltammetric procedure for trace determination of Cr(VI) in natural samples containing high concentrations of humic substances has been developed. The procedure for chromium determination in the presence of DTPA and nitrates was employed as the initial method. In order to enhance the selectivity vs. Cr(III) the measurements were performed at 40°C. Interference from dissolved organic matter such as humic and fulvic acids was drastically decreased by adding Amberlite XAD-7 resin to the voltammetric cell before the deaeration step. The whole procedure was applied to a single cell, which allowed monitoring of the voltammetric scan. Optimum conditions for removing humic and fulvic acids due to their adsorption on XAD-7 resin were evaluated. The use of XAD-7 resin also minimize interferences from various cationic, anionic, and nonionic surfactants. The calibration graph for Cr(VI) for an accumulation time of 30 s was linear in the range 5 × 10⁻¹⁰ to 5 × 10⁻⁸ mol L⁻¹. The relative standard deviation for determination of Cr(VI) at a concentration of 1 × 10⁻⁸ mol L⁻¹ was 3.5% (n = 5). The detection limit estimated from 3 times the standard deviation for low Cr(VI) concentrations and an accumulation time of 30 s was about 1.3 × 10⁻¹⁰ mol L⁻¹. The proposed method was successfully applied to Cr(VI) determination at trace levels in soil samples.     

Cr(III)/Cr(VI) speciation in aerosol particles by extractive separation and thermal ionization isotope dilution mass spectrometry

 An isotope dilution mass spectrometric (IDMS) method, using the formation of positive thermal ions, was developed for Cr(III) and Cr(VI) speciation in aerosol particles. Cr(III) and Cr(VI) spike species, enriched in ⁵³Cr, were applied for the isotope dilution step. After leaching of filter collected aerosol samples by an alkaline solution at pH 13, species separation was carried out by extraction with a liquid anion exchanger in methyl isobutyl ketone. Cr(VI) in the organic phase was re-extracted into an ammoniacal solution and chromium was then isolated from both fractions of species by electrodeposition. Detection limits of 30 pg/m³ for Cr(III) and of 8 pg/m³ for Cr(VI) were achieved in atmospheric aerosols for volumes of air samples of about 120 m³. These low detection limits allowed the determination of chromium species in continental aerosol particles in dependence on different seasons. The Cr(III) /Cr(VI) ratio was always found to be about 0.3 whereas dust from soil erosion, which is probably the primary source of chromium in the atmosphere, showed higher ratios. This indicates that chromium is oxidized in the atmosphere. The accuracy of the method was demonstrated in two interlaboratory comparisons of Cr(VI) determinations in welding dust samples. The IDMS method also contributed to the certification of a corresponding standard reference material organized by the Standard Reference Bureau of the European Union. Chromium speciation, including the determination of elemental chromium Cr(0), was carried out in aerosols of different welding processes for stainless steel. These analyses showed distinct differences in the distribution of chromium species in the welding process and can be used as an exact calibration method for routine methods in this important field of monitoring corresponding working places. Received: 19 August 1996/Revised: 24 September 1996/Accepted: 28 September 1996     

Speciation of Cr(III) and Cr(VI) ions using a β-cyclodextrin-crosslinked polymer micro-column and graphite furnace atomic absorption spectrometry

A sensitive and selective method for the speciation of Cr(III) and Cr(VI) in water samples was developed. It is based on the selective binding of the complex formed between Cr(III) and 4-(2-pyridylazo)resorcinol adsorbed on a cross-linked polymer modified with β-cyclodextrin and placed in a micro-column. Graphite furnace atomic absorption spectrometry (GFAAS) was used to quantify chromium. Cr(VI) ion is not adsorbed but remains in the aqueous sample phase. Thus, an in-situ separation of Cr(VI) and Cr(III) is accomplished. The concentration of Cr (VI) was calculated by subtracting the value for Cr(III) from that for total chromium. Under optimum conditions, the limit of detection of Cr(III) is 0.056 μg L^?1, and the linear range is from 2.0 to 160.0 μg L^?1. The relative standard deviation is 2.5% (n?=?3, at 30.0 μg L^?1). The preconcentration factor is 25. The method was applied to the speciation of chromium in water samples, and recoveries in spiked real samples range from 101.9% to 104.5%. A reference water sample (GBW(E)080642) also was analyzed, and the results were in good agreement with the certified values.

An “off–on” fluorescence probe for chromium(III) ion determination in aqueous solution

An “off–on” rhodamine-based fluorescence probe for the selective signaling of Cr(III) has been designed by exploiting the guest-induced structure transform mechanism. This system shows a sharp Cr(III)-selective fluorescence enhancement response in 100% aqueous system under physiological pH value and possesses high selectivity against the background of environmentally and biologically relevant metal ions including Cr(VI), Al(III), Fe(III), Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I). Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to Cr(III) concentration from 5.0 × 10⁻⁸ to 7.0 × 10⁻⁶ mol L⁻¹ with a detection limit of 1.6 × 10⁻⁸ mol L⁻¹.     

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.     

Chromium speciation,selective extraction and preconcentration by alumina-functionalised 2-pyridenecarboxyladehyde thiosemicarbazone

A method is proposed and explored for speciation of Cr(III) and Cr(VI), selective extraction and preconcentration in various water samples based on dynamic and static techniques. Three newly designed alumina phases-physically adsorbed-2-pyridenecarboxyladehyde-thiosemicarbazone [Al-2PC-TSC (I–III)] were synthesised and characterised. Stability tests and application of [Al-2PC-TSC (I–III)] as inorganic ion exchangers and chelating solid sorbents for various metal ions were studied and evaluated. The distribution coefficient and separation factors of chromium species versus other interfering metal ions were determined to examine the incorporated selectivity into these alumina phases. Quantitative recovery of Cr(VI) was accomplished by [Al-2PC-TSC (I–III)] at pH = 1.0 while Cr(III) was found to be quantitatively recovered on these sorbents at pH = 7.0 with minimal or no interference between these two species under the studied buffering conditions. Selective solid phase speciation and preconcentration of Cr(III) and Cr(VI) in various real water samples were successfully performed and accomplished via a micro-column, with 200 as a preconcentration factor. Selective speciation of Cr(VI) and Cr(III) via preconcentration from seawater and industrial water samples by alumina phases in pH = 1 was found to give percentage recovery values of Cr(VI) in the range 93.5–97.3 ± 3.0–5.0% and 94.0–97.5 ± 3.0–4.0%, for seawater and industrial water samples, respectively.     

Adsorption of metal anions of vanadium(V) and chromium(VI) on Zr(IV)-impregnated collagen fiber

The metal anions of vanadium (V) and chromium (VI) in aqueous solution can be effectively adsorbed by Zr(IV)-impregnated collagen fiber (ZrICF). The maximum adsorption capacity of V(V) takes place within the pH range of 5.0 to 8.0, while that of Cr(VI) is within the pH range of 6.0 to 9.0. When the initial concentration of metal ions was 2.00 mmol L⁻¹ and the temperature was 303 K, the adsorption capacity of V(V) on Zr-ICF was 1.92 mmol g⁻¹ at pH 5.0, and the adsorption capacity of Cr(VI) was 0.53 mmol g⁻¹ at pH 7.0. As temperature increased, the adsorption capacity of V(V) increased, while that of Cr(VI) was almost unchanged. The adsorption isotherms of the anionic species of V(V) and Cr(VI) can be fit by the Langmuir equation. The adsorption rate of V(V) follows the pseudo-first-order rate model, while the adsorption rate of Cr(VI) follows the pseudo-second-order rate model. Furthermore, ZrICF shows high adsorption selectivity to V(V) in the mixture solution of V(V) and Cr(VI). Practical applications of ZrICF could be expected in consideration of its performance in adsorption of V(V) and Cr(VI).     

Ammonium pyrrolidinedithiocarbamate-modified activated carbon micro-column extraction for the determination of As(III) in water by graphite furnace atomic absorption spectrometry

A simple and selective method using ammonium pyrrolidinedithiocarbamate modified activated carbon (APDC-AC) as solid phase extractant has been developed for speciation of As(III) in water samples. At pH 1.8–3.0, As(III) could be adsorbed quantitatively by APDC-AC, and then eluted completely with 2.0 mL of 0.1 mol L⁻¹ HNO₃, while As(V) could almost not be retained at pH 1–7. Effects of acidity, sample flow rate, concentration of elution solution and interfering ions on the recovery of As(III) have been systematically investigated. Under the optimal conditions, the adsorption capacity of APDC-AC for As(III) is 7.3 mg g⁻¹. The detection limit (3σ) of As(III) is 0.05 ng mL⁻¹ for graphite furnace atomic absorption spectrometry (GFAAS) with enrichment factor of 50, and the relative standard deviation (RSD) is 4.1% (n = 9, C = 5 ng mL⁻¹). The method has been applied to the determination of trace As(III) in water, and the recoveries of As(III) are 100 ± 10%. Correspondence: Yiwei Wu, Department of Chemistry and Environmental Engineering, Hubei Normal University, Huangshi 435002, P.R. China     

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 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%.     

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.     

Speciation of Cr(III) and Cr(VI) in waters using immobilized moss and determination by ICP-MS and FAAS

The possibility of using moss (Funaria hygrometrica), immobilized in a polysilicate matrix as substrate for speciation of Cr(III) and Cr(VI) in various water samples has been investigated. Experiments were performed to optimize conditions such as pH, amount of sorbent and flow rate, to achieve the quantitative separation of Cr(III) and Cr(VI). During all the steps of the separation process, Cr(III) was selectively sorbed on the column of immobilized moss in the pH range of 4-8 while, Cr(VI) was found to remain in solution. The retained Cr(III) was subsequently eluted with 10 ml of 2 mol l⁻¹ HNO₃. A pre-concentration factor of about 20 was achieved for Cr(III) when, 200 ml of water was passed. The immobilized moss was packed in a home made mini-column and incorporated in flow injection system for obtaining calibration plots for both Cr(III) and Cr(VI) at low ppb levels that were compared with the plots obtained without column. After separation, the chromium (Cr) species were determined by inductively coupled plasma mass spectrometry (ICP-MS) and flame atomic absorption spectrometry (FAAS). The sorption capacity of the immobilized moss was found to be ∼11.5 mg g⁻¹ for Cr(III). The effect of various interfering ions has also been studied. The proposed method was applied successfully for the determination of Cr(III) and Cr(VI) in spiked and real wastewater samples and recoveries were found to be >95%.