Speciation Determination of Chromium(VI) and Chromium(III) in Soil Samples after Cloud Point Extraction

Abstract

To measure the different activity of chromium(VI) and chromium(III) in soil samples, chromium(VI) and total chromium (CrVI + CrIII) was extracted by KCl extracting agent and alkali fusion, respectively. Cloud point extraction (CPE) for speciation determination of chromium with double-slotted quartz tube atom trap–flame atomic absorption spectrometry (STAT-FAAS) was developed. Preconcentration of chromium(VI) and total chromium in different pH solutions was achieved by CPE, with ammonium pyrrolidine dithiocarbamate (APDC) as the chelating agent and Triton X-114 as the cloud point extractant. The conditions of CPE and determination were studied. Under the optimal conditions, the enrichment factor was 50 for chromium from the initial 100-mL sample solution to the final 2-mL determined solution. Compared to the FAAS method, the sensitivity was improved seven-fold for chromium by the STAT-FAAS method. The limit of detection was 0.082 µg/L for chromium.     

Preconcentration and Spectrophotometric Determination of Chromium (VI) and Total Chromium in Drinking Water by the Sorption of Chromium Diphenylcarbazone with Surfactant Coated Alumina

Abstract

A simple and inexpensive method for determining chromium (VI) in drinking water by spectrophotometry after preconcentration with sodium dodecyl sulphate (SDS) coated alumina column is described. Chromium(VI) is reacted with diphenylcarbazide (DPC) and the Cr-DPC complex is quantitatively adsorbed onto a SDS coated alumina column from 800 ml of sample solution. The complex is then eluted with a 8 ml mixture of methanol, acetone and hydrochloric acid and determined by spectrophotometry. Total chromium can be determined after oxidation of chromium (III) to chromium (VI) by KMnO₄. The relative standard deviation (10 replicate analyses) at the 10 μg l^?1 of chromium (VI) and 10 μg l^?1 of total chromium were 3.5% and 3.4% and corresponding limits of detection (based on 3 σ) were 0.040 μg l^?1 and 0.033 μg l^?1, respectively.     

Coulometric Determination of Chromium(VI) and Copper(II) Present Simultaneously

It was shown that chromium(VI) can be determined by coulometry at a Pt electrode in HNO₃and H₂SO₄solutions. A procedure for the determination of 1–4 mg of chromium in 0.5–1 M HNO₃solutions by controlled-potential coulometry with RSD = 0.2% was developed. It was demonstrated that the degree of the reduction of Cr(VI) to Cr(III) reached 99% (RSD = 0.5%) in the determination of chromium by coulometry at a slow potential sweep (v= 1–2 mV/s) in HNO₃solutions. A procedure was proposed for the determination of Cr(VI) and Cu(II) simultaneously present in 0.25–0.5 M H₂SO₄solutions by controlled-potential coulometry with RSD = 0.3%.     

Flame Atomic Absorption Spectrometric Determination of Total Chromium and Cr(VI) in Cigarette Ash and Smoke using Flow Injection/Hydraulic High-Pressure Sample Introduction

Total chromium and Cr(VI) contents of cigarettes, ash, and smoke formed while burning cigarettes were determined. The determinations of chromium species were carried out according to procedures developed earlier. Cr(VI) was determined in a combined system, which involves a flow injection (FI) sorption preconcentration system, hydraulic high-pressure nebulization (HHPN) sample introduction technique, and flame atomic absorption spectrometric (FAAS) detection. The total chromium of samples in Cr(VI) form was determined in this same combined system after ashing cigarettes at 800°C [after total conversion of Cr(III) of the sample to Cr(VI)]. It was found that while burning cigarettes 0.8–1.2% of the original chromium content of the cigarettes comes to smoke in the toxic Cr(VI) form.     

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.     

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.     

Preconcentration and spectrophotometric determination of chromium(vi) in natural waters by coprecipitation with barium sulfate

A selective preconcentration of chromium(VI) is proposed for analysis of natural waters. Chromium(VI) is quantitatively separated from chromium(III) by coprecipitation with barium sulfate; salicylic acid is used as a masking agent for iron(III), aluminum(III) and chromium(III). The precipitate is fused with alkali carbonate, and the chromium(VI) in the melt is isolated with hot water and determined spectrophotometrically with diphenylcarbazide. The detection limit is 0.02 μg l^-1 the relative standard deviation for chromium(VI) in river water is less than 5%.     

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) and Chromium(IV) Tetraphenylporphine Complexes

Stable chromium complex (AcO)CrTPP was synthesized through the reaction of meso-tetraphenylporphine with chromium(III) acetate in boiling phenol. Coordination properties of chromium porphyrin in reaction with imidazole and pyridine in o-xylene were studied by electronic absorption spectroscopy and computer modeling. A single-electron oxidation of chromium(III) complex was found to be affected by peroxide compounds. The stability of an extra complex depends on the basic properties of the extra ligand and oxidation number of the central metal atom. The complex stability correlates with the calculated energy of formation of the metal–extra ligand bond. The geometrical structure and energy parameters of hexacoordinated chromium porphyrins were calculated using the quantum-chemical method. The effect of the cis and trans position of ligands in the composition of a macrocyclic compound was established to be significant only in the extra complexes (AcO)CrTPP.     

Speciation of Chromium in Natural Waters,Tea, and Soil with Membrane Filtration Flame Atomic Absorption Spectrometry

A sensitive and selective method was developed for the speciation of chromium(III) and chromium(VI) in environmental samples based on membrane filtration and determination by flame atomic absorption spectrometry. Chromium(III) reacts with cochineal red A, yielding a complex that is adsorbed on a cellulose acetate membrane filter, whereas chromium(VI) remains in aqueous solution, permitting separation. After reduction of chromium(VI) to chromium(III) with hydroxylamine hydrochloride, the total concentration of chromium was determined, and the concentration of chromium(VI) was calculated by subtraction. The pH, amount of cochineal red A, and sample volume were optimized on the basis of the recovery of Cr(III). The influence of matrix ions was also investigated. The preconcentration factor was 94. The detection limit (3 sigma) for Cr(III) was 1.4 micrograms per liter. The method was validated using environmental certified reference materials. The method was successfully employed for the speciation of chromium in wastewater and lake water.     

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.     

Chromium speciation and preconcentration using zirconium(IV) and zirconium(IV) phosphate chemically immobilized onto silica gel surface using a flow system and F AAS

A procedure for chromium speciation by F AAS using a flow system has been proposed. In this system, Cr(III) and Cr(VI) ions were adsorbed sequentially onto a mini-column packed with silica gel modified with zirconium phosphate and a mini-column packed with silica gel modified with zirconium oxide, respectively. The elution of Cr(III) and Cr(VI) was made with, respectively, nitric acid solution and tris(hydroxymethyl)methylamine (THAM) solution in reverse mode and determination by flame atomic absorption spectrometry without interference of the matrix. Chemical and flow variables as well as concomitant ions were studied in the developed procedure. The enrichment factor for Cr(III) and Cr(VI) was 20.8 and 24.9, respectively, using a preconcentration time of 3.75 min. The limit of detection for Cr(III) and Cr(VI) was 1.9, and 2.3 μg l⁻¹, respectively. The precision of the method, evaluated as the relative standard deviation in solutions containing 100 μg l⁻¹ of chromium species, by analyzing a series of seven replicates, was lower than 3.0%. The accuracy was assessed through recovery experiments of water samples and using another methodology.     

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.     

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 of chromium(III) and chromium(VI) in sea water by complexation with quinolin-8-ol and adsorption on macroporous resin

Chromium(III) is a sea water at the nanomole level was selectively collected using a column packed with macroporous polystyrene-divinylbenzene resin after complexation with quinolin-8-ol. Complex formation between ligand and inert hydrated chromium(III) ions was achieved by heating a sample solution containing a small amount of quinolin-8-ol for a short time in a microwave oven. Chromium(VI) was collected by a similar method after reducing it to chromium(III) with hydroxylamine. The effect of co-existing organic materials on the collection of chromium(III) and chromium(VI) was examined. This method was successfully applied to the determination of chromium(III) and chromium(VI) in sea water by graphite furnace AAS.     

The Cumulation of Chromium and Arsenic Species in Fish (Poecilia reticulata)

Abstract

Chromium-51 and arsenic-74 were used for the investigation of the uptake and the release of different chromium and arsenic species in fish. It has been found that only trimethylarsine can be rapidly taken up directly from water. The release of chromium(III), consumed by fish in food, is very rapid: about 99.9% of chromium is released within a few days. The same results were obtained with chromium(III) acetylacetonate or chromium(III) ethylenediaminotetraacetate. About 95% of arsenic acid, methylarsonic acid, dimethylarsinic acid or arsenic(III) diethyldithiocarbamate are released within a few days whereas the remaining arsenic is released with the biological half time 35 ± 5 days.     

Preconcentrative separation of chromium(VI) species from chromium(III) by coprecipitation of its ethyl xanthate complex onto naphthalene

A rapid, sensitive and selective method is described for the determination of chromium(VI) in presence of 100-fold amounts of chromium(III) by flame atomic absorption spectrometry (FAAS) in conjunction with coprecipitative preconcentration of its ethyl xanthate complex onto naphthalene. The solid mixture consisting of the chromium(VI) complex together with naphthalene is dissolved in 8.0 ml of dimethyl formamide (DMF) and chromium(VI) content was established by FAAS. Calibration graphs were rectilinear over the chromium(VI) concentration in the range 0-200 μg l⁻¹. Five replicate determinations of 20 μg of chromium(VI) present in 1.0 l of sample solution gave a relative standard deviation of 3.1%. The detection limit corresponding to three times the standard deviation of the blank was found to be 0.5 μg l⁻¹. The developed procedure has been successfully utilized for the estimation of chromium(VI), chromium(total) (after oxidation with bromate) and chromium(III) (by subtracting chromium(VI) content from chromium(total) value contents of several tannery industries.     

Ultrafast concentration and speciation of chromium(III) and (VI)

There is an increasing need to know the concentrations of chromium(III) and (VI) separately rather than only the total chromium content. A method is described for accomplishing this very quickly using only low-cost, portable equipment. Two small, resin-loaded extraction disks are placed one on top of the other in a plastic holder. Then a syringe containing the aqueous sample is attached to the holder and the sample is pushed through the disks. In a matter of seconds, all of the chromium(VI) is retained on the top anion-exchange disk and chromium(III) is extracted by the second cation-exchange disk. The concentrations on each disk are several hundredfold higher than they were in the original sample. The amounts of chromium(III) and (VI) extracted are measured directly on the surface of the respective disks by diffuse reflectance spectroscopy (DRS). Despite the low molar absorptivity of chromium(III) in aqueous solution, the concentration on the upper most layer on the extraction disk is high enough to permit the determination of chromium(III) in samples at the low mg/L range. Chromium(VI) can also be determined at low to sub-mg/L concentrations. A study of the cation-exchange disks was undertaken to compare the performance characteristics of disks containing sulfonated resins and those with iminodiacetate functionality. In addition, data are presented to show the effects of heating the iminodiacetate disks after the initial extraction. The disks were heated in hot water for 15-30 min to complete the slow complexation reaction on the surface.     

Chromium speciation study in polluted waters using catalytic adsorptive stripping voltammetry and tangential flow filtration

The catalytic adsorptive stripping voltammetry (CAdSV) has been applied to physico-chemical chromium speciation study in the upper Dunajec catchment, severely polluted by the tannery wastewater. The method is based on the adsorptive preconcentration of the Cr(III)-diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid (DTPA) complex and the utilization of the catalytic reaction in the presence of nitrate. Under optimized conditions the CAdSV enables the oxidation state speciation study of Cr content by direct determination of Cr(VI) in the presence of the predominant Cr(III) concentration with the detection limit for chromium(VI) of 0.08 nM and the linearity range from 0.1 to 80 nM obtained for 20 s of accumulation, as well as the determination of total Cr after UV oxidation of Cr(III) to Cr(VI). Due to the difference in the chemical properties of different chromium species the CAdSV method makes possible a speciation study of Cr(III) and Cr(VI) oxidation state. The RSD of the determination of Cr(VI) and Cr(III) varies from 0.5 to 5%. It has been proved that in natural water in which strong complexants of Cr(III) such a humid acids are presented, Cr(VI) can be determined accurately in the presence of high excess of Cr(III). Fractionation of selected water samples with tangential flow filtration (TFF, cut-off 10 and/or 1 kDa) provides insight into physical Cr speciation, i.e. partitioning of the Cr(VI) and Cr(III) between the colloidal and the dissolved fractions. It has been shown that the content of the Cr species in the Dunajec river depends on the season, and is significantly higher in autumn and winter during the most intensive tanneries production processes. The concentration of total Cr exceeds occasionally the legally admissible level. A large fraction of total Cr(III) concentration is associated with the colloidal material, while Cr(VI) occurs solely in the truly dissolved form.     

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.