Determination of trace concentrations of hexavalent chromium

A simple and sensitive solvent extraction-atomic spectrometric technique has been developed for the determination of hexavalent chromium in fresh and saline waters. The technique is based on the reaction of chromium with diphenylcarbazide. The method has been tested on a variety of water samples over an analytical range of 0-2 microg l(-1). A limit of detection of 0.024 microg l(-1) was achieved. Spiking recoveries in the range 87-115% were achieved in river water, drinking water and marine waters.     

Analytical properties of 5,5-dimetyl 1,3-cyclohexanedione dithiosemicarbazone monohydrochloride; spectrophotometric determination of chromium(VI) in alloy steels and industrial effluents

The analytical properties of 5,5-dimethyl 1,3-cyclohexanedione dithiosemicarbazone monohydrochloride (5,5-DiMe-1,3-CHDT.HCl) are described. The reagent gives pink coloured solutions with chromium(VI) in acetic medium. The maximum colour intensity is observed in 0.5-2.5 pH range. This colour reaction (molar absorptivity, 1.63 x 10(4) 1 mol(-1) cm(-1) at 360 nm) has been used for the spectrophotometric determination of total chromium in alloy steels and industrial effluents.     

Spectrophotometric determination of chromium in waste water and soil

The reaction of Cr(VI) with o-nitrophenylfluorone (NPF) in presence of cetyltrimethyl-ammonium bromide (CTMAB) to form a purplish red complex at pH 4.7-6.6 by heating at 50 degrees for 10 min has been investigated. The composition of the complex is 1:2:2 [Cr(VI):NPF:CTMAB], the wavelength of maximum absorbance is 582 nm. The molar absorptivity is 1.11 x 10(5)1.mole(-1).cm(-1). Beer's law is obeyed up to 0.2 microg ml Cr(VI) concentration. The interference of several ions, including Cu(2+), Fe(3+) and Al(3+), is eliminated by addition of a masking mixture containing KF, DCTA and tartrate. A new sensitive method for determination of chromium in waste water and soil is presented.     

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.     

Preconcentration of chromium(III) and speciation of chromium by electrothermal atomic absorption spectrometry using cellulose adsorbent

A simple and sensitive method has been developed for species selective determination of chromium(III) and chromium(VI) in water by electrothermal atomic absorption spectrometry. The procedure is based on selective absorption of Cr(III) on a cellulose micro column (pH 11, 0.5 mol L(-1) NaCl). Total chromium was subsequently determined after appropriate reduction of Cr(VI) to Cr(III). Recoveries of more than 97% were found. A concentration factor of 100 was achieved. The relative standard deviations (n=10) at the 40 ng L(-1) level for chromium(III) and chromium(VI) were 2.3% and 1.8% and corresponding limits of detection (based on 36) were 1.8 ng L(-1) and 5.1 ng L(-1), respectively. No interference effects have been observed from other investigated species and the method has been successfully applied to natural water samples.     

Oxidation of l-methionine with aqueous chromic acid: a kinetic study

The kinetics of oxidation of l-methionine by chromic acid in acidic medium (pH=0.83–2.2) has been studied spectrophotometrically. The effect of l-methionine and chromium(VI) concentrations on the rate of the reaction was determined. The reaction rate decreases with increasing the pH of the medium. The kinetics of the formation of a chromium(III) complex conform to the rate law:with k1=7.5×10–2s–1 and Kes1=43.85 at constant [H+]=1.9×10–2moldm–3 and [l-methionine]T= 2.0×10–2moldm–3. The same values were found with [l-methionine]T variation at constant [H+]. The reaction proceeds through formation of chromium(VI)-l-methionine ester in a rapid pre-equilibrium step, followed by a slower redox reaction of the ester. The present study provides kinetic evidence for formation of a complex ion (ester). One mole of Cr2O72– oxidizes four moles of l-methionine, which acts as a monodentate ligand and binds to chromium(VI) through the sulfur atom. The coordinated sulfur atom of l-methionine–chromium(VI) ester is responsible for the oxidative degradation (breaking of the C1-C2 bond) of l-methionine. Coordinated oxygen of the carboxylate group inhibits the cleavage of the C1-C2 bond.     

Synchronous fluorescence and absorbance dynamic liquid drop sensor for cr(VI) determination at the femtomole level

A novel synchronous fluorimetric and absorptiometric technique based on dynamic liquid drops coupled with flow injection is described for the determination of chromium(VI) in aqueous solutions. Drops formed continuously at the end of a quartz capillary tube serve as reactor and optical cell. The reaction between chromium(VI) and 3,3',5,5'-tetramethylbenzidine dichloride (TMB-d) results in a significant decrease in fluorescence and transmitted light intensity, proportional to the logarithm of the concentration of chromium(VI). The transmitted light and fluorescence emission are detected in counter and perpendicular positions of the excitation light by a photomultipler tube and photodiode, respectively. In HCl-NaOAc buffer solution (pH 3.29), the sensor has a wide linear calibration range of 2 x 10(-8)-1 x 10(-4) mol l(-1) chromium(VI) with an absolute mass detection limit of 12.88 fmol.     

Flow injection determination of chromium(III) by pyrogallol chemiluminescence

A flow injection method is proposed for the determination of nanogram amounts of chromium(III) using a pyrogallol chemiluminescence system. It is based on its catalytic effect on the oxidation of pyrogallol with periodate at a neutral medium. The addition of 3-(N-morpholino)propanesulphonic acid to the reaction system increased the chemiluminescence signal for chromium(III). The present method allows the determination of 5-100ng/ml of chromium(III). The relative standard deviation of 2.2% (n = 10) was obtained at 20 ng/ml of chromium(III) and the detection limit (signal-to-noise ratio = 2) was 1 ng/ml with the sampling frequency of 25/hr.     

Determination of 2-Acetyl-1-pyrroline via a Color-Change Reaction Using Chromium Hexacarbonyl

At present, there is no colorimetric method for the quantitation of the aroma compound 2-acetyl-1-pyrroline (2AP). A novel colorimetric method was developed for the determination of 2AP content using chromium hexacarbonyl (Cr(CO)₆) as a reagent. The reaction of synthetic 2AP with chromium hexacarbonyl reagent solution in the presence of light produced a green product with an absorption maximum (λ_max) at 623 nm. GC–MS was used to confirm the color-change reaction, which showed the loss of 2AP after the addition of Cr(CO)₆. This novel method enables facile and cost-effective determination of 2AP in fragrant rice. A comparative analysis of fragrant and nonfragrant rice grain extracts showed that no color-change reaction occurred with the nonfragrant rice sample. A limit of detection (LOD) of 2.00 mg L⁻¹ was determined by method validation with an effective linear concentration ranging from 5.00 to 60.00 mg L⁻¹ of 2AP. The results obtained using the developed colorimetric method were consistent with those obtained by automated static headspace gas chromatography with nitrogen-phosphorus detection (SHS-GC–NPD).     

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.     

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.     

DCB-偶氮胂高灵敏光度法测定痕量铬(Ⅵ)

本文研究了 DCB偶氮胂与 Cr2 O2 - 7的褪色反应。结果表明 ,在硝酸介质中褪色反应具有高的灵敏度 ,拟定了反应的最佳条件 ,建立了一种新的光度法测定痕量铬( )方法。本法检出限为 4.2 2× 1 0 - 11g/m L ,线性范围为 0～ 0 .8μg/1 0 m L ,用于测定人发中的痕量铬 ( ) ,结果令人满意     

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.     

Highly functionalized five-membered carbocycles from (3-dialkylamino-1-ethoxyalkenylidene)pentacarbonylchromium complexes and alkynes: the effects of substituents, solvents, ligand additives, and reagent concentrations on the product distribution

The cocyclization reaction of pentacarbonyl(beta-amino-1-ethoxyalkenylidene)chromium complexes 1 with alkynes has been studied with respect to the effects of substituents, solvents, ligand additives, and reagent concentrations upon the product distribution. This reaction proceeds either as a formal [2 + 2 + 1] cycloaddition to give 5-(1'-dialkylaminoalkylidene)-4-ethoxycyclopent-2-enones 8 or a formal [3 + 2] cycloaddition to give 5-dialkylamino-3-ethoxy-1,3-cyclopentadienes 9. A working hypothesis for the mechanism of this reaction is proposed on the basis of that previously determined for the D?tz reaction. The effects of the aforementioned parameters upon the product distribution of this current reaction are explained in terms of this model. A pronounced ligand-induced allochemical effect has been observed. Conditions for the selective preparation of both classes of cycloadducts 8 and 9 have been determined.     

Spectrophotometric determination of vanadium with 1,10-phenanthroline

A simple and sensitive spectrophotometric method for the determination of vanadium based upon the reaction of vanadate with 1,10-phenanthroline in the presence of sodium dithionite in ammoniacal solution is described. The absorbance of the complex measured at 645 nm follows Beer's law for solutions containing 30-400 microg of vanadium in 100 ml of solution. A 10-fold excess of molybdenum, tungsten, phosphorus or chromium does not interfere. The molar absorptivity is 8.0 x 10(3) 1 mole(-1) cm(-1). The complex is shown to be tris-1,10-phenanthroline vanadium(II). The method has been applied successfully to the determination of vanadium in bauxite.     

催化动力学荧光法测定眼影中的铬(Ⅵ)

在酸性介质中, 痕量Cr(Ⅵ)对高碘酸钾氧化罗丹明B的褪色反应有催化作用, 使罗丹明B的荧光减弱, 据此建立了催化动力学荧光法测定痕量Cr(Ⅵ)的新方法. 考察了该催化反应的最佳条件, 在最优化条件下, Cr(Ⅵ)质量浓度在1×10-8～7×10-7 g/L范围内与荧光强度呈良好的线性关系, 方法的检出限为3×10-9 g/L, 对1×10-7 g/L的Cr(Ⅵ)标准溶液进行11次平行测定, 得相对标准偏差(RSD)为1.4%. 该法已用于眼影中Cr(Ⅵ)含量的测定, 回收率为97.4%～102.6%.     

Synthesis of optically active organoantimony compounds having an (S)-alpha-methylbenzyldimethylamine group and its evaluation for asymmetric reaction

Novel, enantiomerically pure organoantimony compounds having a C-chiral amine moiety, (S)-(alpha-methyl-2-di-p-tolylstibanobenzyl)dimethylamine [AMSb] (2) and its (eta(6)-arene)chromium complex [AMSb-Cr(CO)(3)] (4), were prepared from common (S)-(alpha-methylbenzyl)dimethylamine (1) via its ortho-lithiated intermediates in short steps. The catalytic activity and enantioselectivity of the ligands 2 and 4 for asymmetric reaction are evaluated, and the optically active (eta(6)-arene)chromium complex 4 has been shown to be an effective ligand for rhodium-catalyzed asymmetric hydrosilylation of ketones.     

一种测定六价铬的新方法

基于六价铬在稀盐酸介质中氧化盐酸羟胺产生亚硝酸根 ,而亚硝酸根可使对硝基苯胺重氮化并与α -萘胺偶联产生红色偶氮染料 ,提出了分光光度法测定六价铬的新方法。在最佳实验条件下 ,六价铬的浓度在0～ 5 0 μg/2 5mL内服从比耳定律 ,其线性相关系数γ为 0 .9990 ,表观摩尔吸光度ε51 0 为 2 .48× 1 0 4 L·mol- 1 ·cm- 1 。所拟方法用于水样中微量铬的测定 ,结果满意     

A highly sensitive colour reaction for chromium(VI) with the iodide-basic xanthene dye-pva system

A highly sensitive spectrophotometric method has been developed for determination of chromium(VI), based on oxidation of I(-) to I(-)(3) in acid medium, then formation of a 1:1 ion-association compound of I(-)(3) with a basic xanthene dye in the presence of poly(vinyl alcohol). The molar absorptivity is 1.79 x 10(5) 1.mole(-1).cm(-1) at 600 nm for the Rhodamine B system, 1.56 x 10(5) 1.mole(-1).cm(-1) at 600 nm with Ethylrhodamine B, 1.56 x 10(5) 1.mole(-).cm(-1) at 570 nm with Rhodamine 6G and 2.01 x 10(5) 1.mole(-1).cm(-1) at 590 nm with Butylrhodamine B, respectively. Preconcentration of chromium(VI) by an improved trioctylamine extraction procedure greatly increases the selectivity of the method and can be applied in the spectrophotometric determination of trace amounts of chromium(VI) in tap water, hot-spring water and river water.