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%.     

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.     

Separation of Cr(III) and Cr(VI) using complexation of Cr(III) with 8-hydroxyquinoline and determination of both species in waters by ETA-AAS

Summary A method for the determination of chromium(III) and (VI) species has been studied and applied to mineral water samples. The chromium(III) was chelated with 0.1 mol/l 8-hydroxyquinoline in methyl alcohol, extracted in isobutyl methyl ketone and determined by ETA-AAS. The effects of the pH, extraction and heating time and amounts of the reagents required for the extraction were studied. A method for the determination of total chromium was optimized too, and the chromium(VI) can be calculated. The precision, sensibility, accuracy, graphite furnace program and interferences for both methods were also investigated.     

Speciation of Cr(III) and Cr(VI) by reversed phase high-performance liquid chromatography using UV-detection

Summary A method for the simultaneous determination of Cr(III) and Cr(VI) in water samples is described. The different reaction products of Cr(III) and Cr(VI) species with ammonium pyrrolidinedithiocarbamate (APDC) are extracted with ethyl acetate and determined by reversed phase HPLC using UV-detection. The procedure is optimized and its detection limit accordingly improved as compared to literature data. The detection limits achieved are 2.4 g/l for Cr(III) and 2.1 g/l for Cr(VI) and the calibration curves are linear between 5 g/l and 5000 g/l. For the speciation of Cr, APDC was demonstrated to be more suitable as chelating agent than sodium diethyldithiocarbamate (NaDDC). The procedure was applied to the determination of both Cr species in galvanic waste waters and its accuracy was approved by comparing the results (at the 100 g/l level) with those of a photometric determination of Cr(VI) species.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Speciation of Cr(VI)/Cr(III) in environmental waters by fluorimetric method using central composite, full and fractional factorial design

In this approach a fluorometric technique has been developed to study chromium speciation, based on optimised conditions using chemometric methods of experimental design and central composite design. Full and fractional factorial design was used for evaluation of the effective factors in determination of Cr(VI) by fluorometric using Rhodamine-6G in the presence of H₂SO₄. Theory and methodology of a central composite design as a chemometric method for the optimisation of analytical procedures were developed in this approach. It was found that the analytical performance for measurement at the point of optimum in this technique is superior and more accurate than that of one variable at a time. Cr(VI) and Cr(III) were measured in a wastewater sample using the proposed technique. The results confirm the selective determination and speciation of Cr(VI)/Cr(III).     

Fluorimetric Cr(VI) and Cr(III) Speciation With Crystal Violet

Abstract

A simple fluorimetric determination of Cr(VI) in the presence of Cr(III) is described. This determination is based on the fluorescence, produced from the ion-association complex between the Crystal violet cation and the anionic complex, formed between Cr(VI) and excess of I^?. This fluorescence is not observed when Cr(III) is used instead of Cr(VI). The fluorescence intensity is linear over the concentration range of 0–60 μg/1. The method was applied in potable and sea waters.     

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.     

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 Cr(III) and Cr(VI) in surface waters with a Chelex-100 resin column and their quantitative determination using inductively coupled plasma mass spectrometry and instrumental neutron activation analysis

Inorganic Cr(III) and Cr(VI) have contrasting biological, geochemical and toxicology effects. Cr(III) is considered as an essential species for the proper functioning of living organisms but Cr(VI) is toxic for the biological systems. An off-line speciation method using Chelex-100 has been practiced for speciation to Cr(III) and Cr(VI) from surface waters of rivers. The underlying principal of this separation method is based on the ability of cationic Cr(III) to be retained by the resin Chelex-100 while the anionic Cr(VI) remained in the sample matrices. The efficiency of this technique was improved by studying the effect of resin pH. Quantitative determination using inductively coupled plasma-mass spectrometry (ICP-MS) and instrumental neutron activation analysis (INAA) was carried out after the separation to determine the total Cr and Cr(VI) in the liquid matrices. The precision and the accuracy of the quantitative analysis were evaluated by using standard reference material NRCC CASS-2 Intercomparison of INAA and ICP-MS results were determined. The quantity of inorganic Cr(III) and Cr(VI) in the surface water of rivers in the vicinity of industrial areas was investigated together with the determination of the physical properties of the water rivers during sampling.     

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.     

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.     

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.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Simultaneous determination of Cr(III) and Cr(VI) with prechelation of Cr(III) using phthalate by ion interaction chromatography with a C-18 column

Ion interaction chromatography has been successfully used for the simultaneous determination of Cr(III) and Cr(VI) in waste water. A C-18 column which had been dynamically coated with octylamine was used for the separation of Cr(III) and Cr(VI) based on anionic interaction. Cr(III) was chelated with potassium hydrogen phthalate (KHP) before injecting into the column since the Cr(III) did not exist in an anionic form like the Cr(VI) (Cr₂O₇²⁻) presented at the optimum condition. The analytes were detected at 200 nm and linear relationship between absorption with the concentration of Cr(III) or Cr(VI) was 0.1-50 mg/L. Most of the interested interferences including alkali metals, heavy metals and organic materials have no significant effect on Cr(III)-KHP complexation and Cr(VI) stability, only NH₄⁺ and ascorbic acid yielded the serious effect on the Cr(VI) stability. The relative standard deviations calculated from both of peak area and retention time were 0.75-2.20%. The sensitivity of the method at the level concentration of sub mg/L enabled the simultaneous determination of Cr(III) and Cr(VI) contents in waste water samples without any special sample preparation step.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 g/l for Cr(VI) and 5 g/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Speciation of Cr(III) and Cr(VI) in water after preconcentration of its 1,5-diphenylcarbazone complex on amberlite XAD-16 resin and determination by FAAS

A simple and sensitive method for the speciation, separation and preconcentration of Cr(VI) and Cr(III) in tap water was developed. Cr(VI) has been separated from Cr(III) and preconcentrated as its 1,5-diphenylcarbazone complex by using a column containing Amberlite XAD-16 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. Then, Cr(III) has been calculated by subtracting Cr(VI) from the total. The effect of acidity, amount of adsorbent, eluent type and flow rate of the sample solution on to the preconcentration procedure has been investigated. The retained Cr(VI) complex was eluated with 10 ml of 0.05 mol l⁻¹ H₂SO₄ solution in methanol. The recovery of Cr(VI) was 99.7±0.7 at 95% confidence level. The highest preconcentration factor was 25 for a 250 ml sample volume. The detection limit of Cr(VI) was found as 45 μg l⁻¹. The adsorption capacity of the resin was found as 0.4 mg g⁻¹ for Cr (VI). The effect of interfering ions has also been studied. The proposed method was applied to tap water samples and chromium species have been determined with the relative error <3%.     

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%.     

On the spectrophotometric flow injection determination of chromium(VI) in natural waters after on-line preconcentration on activated alumina

The feasibility of chromium(VI) preconcentration on to activated alumina in a continuous flow system with spectrophotometric detection was investigated. Chemical and flow variables, and the influence of concomitant species were studied both with and without preconcentration systems. The best results were obtained by using a 2.5 cm long, 1.6 mm i.d. alumina minicolumn, and selecting 1 x 10(-4) M nitric acid as the preconcentrating medium and 0.1 M ammonium hydroxide as the eluent. The eluted chromium(VI) was mixed with diphenylcarbazide in acidic medium and the absorbance of the colored complex was measured at 540 nm. Linear calibrations for 5, 25 and 50 ml sample volumes were established over the concentration ranges 10-50 mug 1(-1), 2-10 mug 1(-1) and 1-5 mug 1(-1) with sensitivity enhancements of 44, 196 and 392 and detection limits (3sigma) of 3.0 mug 1(-1), 0.3 mug 1(-1) and 0.2 mug 1(-1), respectively. The methods is relatively fast and cheap. Natural waters were analyzed with use of the developed procedure.     

Protocol for Extraction and Determination of Cr(VI) in Solid Materials with a High Cr(III)/Cr(VI) Ratio Using EDDS as a Leaching Agent for Cr(VI) and a Masking Agent for Cr(III)

A sensitive and selective protocol for the extraction of all forms of Cr(VI) from solid materials followed by determination by catalytic adsorptive stripping voltammetry has been elaborated. Cr(VI) was leached to a solution with 0.2 mol L^?1 (NH₄)₂SO₄/NH₄OH+0.1 mol L^?1 EDDS (pH 9.5) and simultaneously Cr(III) was transferred to a nonactive electrochemical complex with EDDS. The method allows for Cr(VI) determination in solid samples containing even a 1000–2000 fold excess of extractable Cr(III) without its noticeable influence. The effects of several experimental variables such as the composition and pH of the extractant, the time and temperature of the solid sample mixing with the extractant were studied. At the optimized conditions more than 95% of total Cr(VI) recoveries from solid samples were achieved. The validation of the proposed procedure was carried out by Cr(VI) determination in certified reference material CRM 019 Ash, spiked and unspiked with Cr(III), and by comparing the obtained results with those obtained using other common extraction procedures.     

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.