Anion-exchange high-performance liquid chromatographic determination of ascorbic acid and hexavalent chromium in rat lung preparations after treatment with sodium chromate in vitro and in vivo

Simultaneous analysis of ascorbic acid and chromium (VI) in soluble fractions and bronchoalveolar lavage fluids of rat lungs treated with sodium chromate in vitro and in vivo was performed by anion-exchange high-performance liquid chromatography coupled to a photodiode-array detector. Absorbances at 265 and 370 nm were used for the determination of ascorbic acid and chromium (VI), respectively. The calibration graphs of standard solutions were linear in the test ranges of ascorbic acid an chromium (VI) (below 10 and 8 ppm, respectively). The detection limits of ascorbic acid and chromium (VI) were 1 and 0.5 ng, respectively. The recovery of ascorbic acid from lung tissues homogenized at pH 7.4 was 99%, and that of chromium (VI) was 96%, when tissues were homogenized under alkaline conditions (pH 11.4). Using this method, ascorbic acid levels in the soluble fractions and lavage fluids of normal rat lungs were determined. In the lung of a rat intratracheally injected with a saline solution of sodium chromate, ascorbic acid decreased to 80% of the normal level, and ca. 90% of the chromium (VI) was reduced within 4 min after injection, indicating that the ascorbic acid-related reduction of chromium (VI) is very rapid. The present method will be useful for studies of the reduction of chromium (VI) by ascorbic acid in biological systems.     

Ammonium hexanitratocerate(IV) as an oxidizing agent-VI Determination of chronuum(III) through oxidation to chromium(VI) at room temperature

A new method has been developed for the determination of chromium(III), depending on its oxidation to chromium(VI) at room temperature by treatment with 50-100% excess of ammonium hexanitratocerate(IV) in 1.0M nitric acid medium. The reaction is complete within 15 min. The unreacted cerium(IV) is titrated potentiometrically with sodium oxalate.     

Disodium-1,8-dihydroxy-naphthalene-3,6-disulphonate (chromotropic salt) as a reagent in inorganic analysis

Summary The compound disodium-1,8-dihydroxy-naphthalene-3,6-disulphonate (sodium salt of chromotropic acid) is employed as a colorimetric reagent for titanium. It is also known to produce coloured complexes with chromium(VI), vanadium and uranium. In the present paper the formation of colour with forty metallic ions has been studied qualitatively, in neutral as well as in alkaline and acidic media. It has been found that the reagent yields coloured complexes with mercury(I), tin(IV), platinum(IV), gold(III), tellurium(VI), molybdenum(VI), iron(III), aluminium(III), chromium(III), and uranyl(II) besides those recorded above.The colour reactions are particularly sensitive to uranyl(II), iron(III), mercury(I), tin(IV), gold(III) und molybdenum(VI).     

Optimization of species stability and interconversion during the complexing reaction for chromium speciation by high‐performance liquid chromatography with inductively coupled plasma mass spectrometry

High‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry was employed for the determination of chromium species. For simultaneous separation of both chromium species by an anion‐exchange column, ethylenediaminetetraacetic acid was induced to form negatively charged complex with Cr(III) normally. Cr(III) chelating reactions are known to be slow, so a high temperature and long reaction time are needed to ensure the completion of the complexing reaction. However, the stability and interconversion of chromium species during the complexing reaction have not been studied earlier. The main aim of this work was to optimize and investigate complexing reaction conditions between ethylenediaminetetraacetic acid and Cr(III). Through optimizing conditions, the reaction will be finished completely in 15 min at pH 7 and 70°C without any obvious interconversion between Cr(VI) and Cr(III). By compromising analysis time, chromatographic resolution, and sensitivity, 60 mM NH₄NO₃ as competing ion concentration and 1.2 mL/min as flow rate have been selected for real‐sample application. Detection limits for Cr(VI) and Cr(III) were 0.051 and 0.078 μg/L, respectively. The proposed method was used for the determination of chromium species in tap and surface water samples with an acceptable range of spiked recoveries of 95–109%.     

A kinetic and mechanistic study of the oxidation of tyrosine by chromium(VI) in aqueous perchloric acid medium

The oxidation of tyrosine by chromium(VI) in aqueous perchloric acid medium has been studied spectrophotometrically at 30 °C and at a constant ionic strength I = 3.10 mol dm⁻³. The main reaction products were identified as chromium(III) and 4-hydroxyphenylacetaldehyde. The stoichiometry is 2:3, i.e., two moles of chromium(VI) react with three moles of tyrosine. The reaction is first order with respect to both chromium(VI) and tyrosine. Increase in perchloric acid concentration increased the rate of reaction. The order with respect to acid concentration was found to be two. Added products, ionic strength and dielectric constant of the medium did not have any significant effect on the reaction rate. A suitable mechanism is proposed. The activation parameters were determined with respect to the slow step of the mechanism. The thermodynamic quantities were also determined and discussed.     

Quantitative analysis of chromium(V) by EPR spectroscopy

A procedure to accurately quantitate chromium(V) in environmental and medicinal chemistry samples was developed using electron paramagnetic resonance spectroscopy (EPRS) as the method of detection. It was found to have an error in the order of +/-10% and a detection limit of 0.010 mM (0.5 mg l(-1)) chromium(V). The method has been used to quantitate the formation of chromium(V) in the interaction of chromium(VI) with fulvic acid and a simple model of this acid, viz, 1.2-dihydroxybenzene. Analysis of solutions obtained from the reaction of 1,2-dihydroxybenzene with chromium(VI) demonstrated that even when the organic substrate was present in a 182-fold excess, the maximum chromium(V) concentration attained represented just 1.44% of the initial chromium(VI). Reactions between chromium(VI) and fulvic acid yielded similar results. It was therefore concluded that at background environmental concentrations of chromium and fulvic acid, the production of chromium(V) is insignificant, however, its possible importance in contaminated systems cannot be disregarded on this basis alone. The method for quantitative analysis reported in this paper should be an invaluable tool for investigations into the significance of chromium(V) in the toxicological mechanism of chromium(VI) and its role as a mutagenic agent.     

Improvement on Simultaneous Determination of Cr(III) and Cr(VI) by Capillary Electrophoresis and Chemiluminescence Detection

Chromiumexistsindifferentoxidationstatesingroundwater,industrialwastewater,seawater,andsoilofourenvironment1,2.Chromium(III)isanessentialtraceelementforhumans,requiredforthemaintenanceofnormalglucose,cholesterol,andfattyacidmetabolism.Ontheotherhand,watersolublechromium(VI),intheformCr2O72-orCrO42-,ishighlyirritatingandtoxictohumansandanimals3.Itsacutetoxiceffectsincludeanimmediatecardiovascularshockandlatereffectsonkidney,liver,andblood-formingorgans.Therefore,itisnecessaryforriskassessme…     

Speciation of chromium (VI) and total chromium determination in welding dust samples by flow-injection analysis coupled to atomic absorption spectrometry

We have studied the speciation of chromium (VI) in stainless-steel welding dusts. The approach used for the analysis of Cr(VI) and total Cr relies on a flow-injection analyzer (FIA) equipped with two different sequential detectors. The system measures Cr(VI). by colorimetry (with 1,5-diphenyl carbohydrazide) and total chromium content by flame atomic absorption spectroscopy (AAS). The extraction of the samples of welding-fume dusts is achieved in a buffer solution (acetic acid and sodium acetate at pH 4). This extraction procedure gives a 96% recovery of chromium (VI). The FIA-AAS system that has been described is also more sensitive, has a lower detection limit (0.005 mug ml(-1)) and gives a better precision (< 1%) than other equivalent systems that have been previously described.     

Speciation of chromium by in-capillary reaction and capillary electrophoresis with chemiluminescence detection

A sensitive method for the simultaneous determination of chromium(III) (Cr3+) and chromium(VI) (CrO4(2-)) using in-capillary reaction, capillary electrophoresis (CE) separation and chemiluminescence (CL) detection was developed. The chemiluminescence reaction was based on luminol oxidation by hydrogen peroxide in basic aqueous solution catalyzed by Cr3+ ion followed by capillary electrophoresis separation. Based on in-capillary reduction, chromium(VI) can be reduced by acidic sodium hydrogensulfite to form chromium(III) while the sample is running through the capillary. Before the electrophoresis procedure, the sample (Cr3+ and CrO4(2-)), buffer and acidic sodium hydrogensulfite solution segments were injected in that order into the capillary, followed by application of an appropriate running voltage between both ends. As both chromium species have opposite charges, Cr3+ ions migrate to the cathode, while CrO4(2-) ions, moving in the opposite direction toward the anode, react with acidic sodium hydrogensulfite which results in the formation of Cr3+ ions. Because of the migration time difference of both Cr3+ ions, Cr(III) and Cr(VI) could be separated. The running buffer was composed of 0.02 mol l(-1) acetate buffer (pH 4.7) with 1 x 10(-3) mol l(-1) EDTA. Parameters affecting CE-CL separation and detection, such as reductant (sodium hydrogensulfite) concentration, mixing mode of the analytes with CL reagent, CL reaction reagent pH and concentration, were optimized. The limits of detection (LODs) of Cr(III) and Cr(VI) were 6 x 10(-13) and 8 x 10(-12) mol l(-1) (S/N=3), respectively. The mass LODs for Cr(III) and Cr(VI) were 1.2 x 10(-20) mol (12 zmol) and 3.8 x 10(-19) mol (380 zmol), respectively.     

Determination of total chromium by flow injection analysis

The determination of total chromium by flow injection analysis is described. Cerium(IV) and nitric acid are used to convert chromium(III) to chromium(VI); the oxidation rate is enhanced by placing the reaction coil in an 80°C oil bath. 1,5-Diphenylcarbazide is used to form a colored complex with chromium(VI) that is measured at 540 nm. For both chromium(III) and chromium(VI), relative standard deviation of less than 1% is achieved with a sampling rate of 40 per hour. Linear response is obtained for 0.5–10 mg l^?1 chromium.     

Application of 2,2′-Diquinoxalyl to the spectrophotometric determination of gold(III) and chromium(VI)

The reaction of 2,2′-diquinoxalyl with tin(II) and titanium(III) was used for spectrophotometric determination of chromium(VI) and gold(III). The conditions of the reactions were determined. The curves for determination of chromium(VI) and gold(III) were found. The influence of foreign ions was examined.     

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.     

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.     

Spectrophotometric micro-method for the determination of ethanol in commercial beverages

 A sensitive spectrophotometric method for the determination of ethanol with potassium dichromate was developed. Chromium(VI), in 7 mol L^-1 perchloric acid, reacts quantitatively with ethanol to form chromium(III) and acetic acid. The reaction is complete in about 15 min at room temperature and the chromium(VI) consumed may be determined by the decrease of the absorbance at 267 nm. The analytical working parameters (such as acidity and ionic strength of the solution, temperature and time of the reaction, chromium(VI) concentration, matrix interferences) were optimized. The apparent molar absorptivities of chromium(VI), in the monomer and dimer form, and the equilibrium quotient for the dimerization reaction were determined in 3 mol L^-1 perchloric acid solution. The method was applied to the analysis of micro samples of commercial beverages (beers, wines and spirits) without the previous distillation of ethanol. Received: 9 April 1996/Revised: 3 June 1996/Accepted: 11 June 1996     

Micellar catalysis on picolinic acid promoted hexavalent chromium oxidation of glycerol

Under pseudo-first-order conditions, monomeric Cr(VI) was found to be kinetically active in the absence of picolinic acid (PA), whereas in the PA-promoted path, the Cr(VI)–PA complex undergoes nucleophilic attack by the substrate to form a ternary complex which subsequently experiences redox decomposition, leading to glyceraldehydes and Cr(IV)–PA complex. The uncatalyzed path shows a second-order dependence on [H⁺], whereas the PA-catalyzed path shows zero-order dependence on [H⁺]. Both the uncatalyzed and PA-catalyzed path show a first-order dependence on [glycerol]_T and [Cr(VI)]_T. The PA-catalyzed path is first order in [PA]_T. All these observations remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant cetyl pyridinium chloride (CPC) and anionic surfactant sodium dodecyl sulfate (SDS) on the PA-catalyzed path have been studied. CPC inhibits, whereas SDS accelerates the reaction. Here, SDS is a catalyst for glyceraldehydes production and at the same time reduction of carcinogenic hexavalent chromium to nontoxic trivalent chromium. The reaction proceeds simultaneously in both aqueous and micellar phase. Micellar effects have been explained by considering the preferential partitioning of reactants between the micellar and aqueous phase. The Menger–Portnoy model, Piszkiewicz cooperative model, and pseudo-phase ion exchange model have been tested to explain the observed micellar effect.     

Iodnitrotetrazolium chloride-A new analytical reagent for determination of chromium

The extraction of chromium (VI) with iodnitrotetrazolium chloride (INT) was studied spectrophotometrically. The basic spectrophotometric characteristics of the ion associated formed were determined. Using different methods it was found that the ratio between chromium and INT was 1:1. The molar absorptivity of the associate is (250) = (3.70 +/- 0.08) x 10(4) 1.mole(-1).cm(-1). Performing the reaction in acid medium (0.1-1.1M hydrochloric acid) allowed the determination of chromium in the presence of large amounts of W(VI), Mo(VI), Fe(III) and V(V). Hence INT is suggested as a sensitive and selective reagent for extractive-spectrophotometric determination of microquantities of chromium(VI).     

Facile Oxidation of Aldehydes to Carboxylic Acids with Chromium(V) Reagents

Recently we reported a convenient method of oxidation of alcohols to carbonyl compounds using chromium(V) reagents.¹ Although a variety of reagents are available for effecting this transformation, there are only a few reagents which have been successfully used for the oxidation of aldehydes to carboxyllc adds. Chromic acid, silver oxide and potassium permanganate are commonly employed for this purpose and reactions are performed in protic media under conditions which are not that mild.² The “non-aqueous” chromium(VI) reagent, pyridinium dichromate, recently reported by Corey³ oxidises alcohols and aldehydes to carboxylic acids in DMF at room temperature. Although Cr(V) species is postulated as an intermediate in all oxidations with Cr(VI), no systematic oxidation studies have been reported with these reagents. This note reports the results of some fruitful investigations on aldehyde → carboxylic acid conversion involving some “non-aqueous” chromium (V) complexes 1, 2, 3 and 5 under anhydrous conditions.     

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.     

Studies on the extraction of chromium(VI) by ketones

A study of the extraction of chromium(VI) from aqueous media by ketones was made. Extraction of chromium was found to be most efficient from aqueous hydrochloric acid solutions. A mechanism for the extraction of chromium(VI) from aqueous hydrochloric acid solutions by methyl isobutyl ketone is proposed involving the formation of a receptor in the organic phase, the exchange of the chloride ion of the receptor for the anionic chromium(VI) species of the aqueous phase, and the solvation of the extracted chromium species. The differences in the abilities of various ketones to extract chromium(VI) from aqueous hydrochloric acid solutions, and the differences in the extraction of chromium (VI) from various aqueous acids by methyl isobutyl ketone are attributed to the differences in the formation of receptors.     

Rapid determination of chromium(VI) in electroplating waste water by use of a spectrophotometric flow injection system

A new rapid and sensitive FI method is reported for spectrophotometric determination of trace chromium(VI) in electroplating waste water. The method is based on the reaction of Cr(VI) with sodium diphenylamine sulfonate (DPH) in acidic medium to form a purple complex (lambda(max) = 550 nm). Under the optimized conditions, the calibration curve is linear in the range 0.04-3.8 microg ml(-1) at a sampling rate of 30 h(-1). The detection limit of the method is 0.0217 microg ml(-1), and the relative standard deviation is 1.1% for eight determinations of 2 microg ml(-1) Cr(VI). The proposed method was applied to the determination of chromium in electroplating waste water with satisfactory results.