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).     

Spectrophotometric determination of vanadium(IV) with nitrilotriacetic acid

A new and convenient spectrophotometric method for the estimation of vanadium(IV) with NTA is described. The minimum ratio of metal ion to ligand, working pH, wavelength for maximum absorbance of the complex ion, and the effect of various cations and anions are described. The complex ion obeys Beer's law in the concentration range 1–32 mmol/liter of the vanadium(IV) ion. It is observed that iron(II), cobalt(II), nickel(II), copper(II), and oxidizing anions such as chromate and nitrite interfere in this determination, whereas managanese(II), chromium(III), iron(III), and anions like nitrate, chloride, bromide, iodide, thiocyanate, sulfate, and sulfite do not have any effect. Excessive amounts of acetate, phosphate, oxalate, tartrate and thiosulfate must also be avoided in this determination. Anions and cations which interfere in the determination of vanadium(IV) by NTA should not be present in the system.     

Adsorptive stripping voltammetric determination of chromium in gallium

The electroanalytical chemistry of trace metals has progressed strongly with the development of cathodic stripping voltammetry (CSV) preceded by adsorption collection of organic metal complexes. A sensitive method for the determination of trace amount of chromium in gallium is described. Gallium is dissolved in sodium hydroxide containing hydrogen peroxide. The method is based on the catalytic activity of nitrate ions on the reduction of Cr(III)TTHA (triethylene tetramine-N,N,N',N',N',N'-hexaacetic acid) complex. The sensitivity of this method is further improved by adsorption preconcentration of Cr(III)TTHA complex at a hanging mercury drop electrode (HMDE). The Cr(III) formed at the electrode surface by the reduction of Cr(VI), which is present in the bulk solution, is immediately complexed by TTHA. The adsorbed complex is then reduced at a peak potential of - 1.26 V, and the peak height of Cr(III) reduction is measured. The determination limit was restricted by the amount of chromium present in the reagent blank solution. The method is suitable for the determination of chromium at level as low as 0.2 mug g(-1) (with about 50 mg of sample) and a relative standard deviation of 15%.     

Determination of trace chromium(VI) by an inhibition-based enzyme biosensor incorporating an electropolymerized aniline membrane and ferrocene as electron transfer mediator

A novel inhibition-based glucose oxidase (GOx) biosensor for environmental chromium(VI) detection is described. An electropolymerized aniline membrane has been prepared on a platinum electrode containing ferrocene as electron transfer mediator, on which GOx is cross-linked by glutaraldehyde. The mechanism of the redox reaction on the electrode and the performance of the sensor are studied. The sensor's response to glucose decreases when it is inhibited by chromium(VI), with a lower detection limit of 0.49?µg?L^?1, and the linear response range is divided into two parts, one of which is 0.49–95.73?µg?L^?1 and the other is 95.73?µg^?1 to8.05?mg?L^?1. The enzyme membrane is shown to be completely reactivated after inhibition, retaining 90% activity over more than forty days. Interference to chromium(VI) determination from lead(II), copper(II), cadmium(II), chromium(III), cobalt(II), tin(II) and nickel(II) is found to be minimal, while high concentrations of mercury(II) and silver(I) may interfere with the determination of trace chromium(VI). The sensor has been used for chromium(VI) determination in soil samples with good results.     

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.     

Analytical speciation of chromium in in-vitro cultures of chromate-resistant filamentous fungi

In this work, different analytical speciation schemes have been used to study the reduction of Cr(VI) by a chromate-resistant strain of filamentous fungi Ed8 (Aspergillus sp), indigenous to contaminated industrial wastes. As demonstrated previously, this strain has the capability to reduce chromate present in the growth medium without its accumulation in the biomass, yet the reduced chromium end-products have not been characterized. Liquid growth medium, initially containing 50 mg L(-1) Cr(VI), was analyzed for Cr(III)/Cr(VI) and for total Cr at different time intervals (0-24 h) after inoculation with fungi. Three hyphenated procedures, based on the Cr(III)-EDTA formation and species separation by anion-exchange or ion-pairing reversed-phase chromatography with ICP-MS or DAD detection were used. The results obtained for Cr(VI) in each case were consistent, demonstrating efficient reduction of chromate during 24 h of Ed8 growth. However, pre-column complexation with EDTA did not ensure complete recovery of the reduced forms of chromium in the above procedures. An alternative speciation scheme, based on extraction of Cr(VI)-benzyltributylammonium bromide (BTAB) ion pairs into chloroform and subsequent determination of residual chromium by ICP-MS has provided evidence on the effective conversion of chromate into reduced chromium species in the growth medium. The results indicate the feasibility of using Ed8 strain for chromate bioremediation purposes. Analytically it can be concluded that speciation of chromium in biological systems should not be limited to its two most common oxidation states, because the actual reduced chromium species are not converted quantitatively to Cr(III)-EDTA.     

Polarography of metal-gallic complexes

The polarographic behavior of metal ions in perchlorate media containing gallic acid is described. Tungsten(VI) forms a complex with gallic acid which yields a single wave in these media, useful in the polarographic determination of tungsten. Evidence for complexation of chromium(III), copper(II), iron(III), molybdenum(VI), uranium(VI), vanadium(V), tungsten(VI), praseodymium(III), samarium(III), neodymium(III) and gadolinium(III) is obtained and the behavior of these metal ions is summarized.     

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.     

Differential determination of antimony(III) and antimony(V) by indirect spectrophotometry with chromium(VI) and diphenylcarbazide,after reduction of antimony(V)

Antimony(III) is determined indirectly through its reaction with excess of chromium(VI), the excess being quantified with diphenylcarbazide and measurement at 540 nm. Antimony(V) is reduced to antimony(III) with sodium sulfite in hydrochloric acid solution; excess of sulfite is eliminated by boiling. The subsequent determination of antimony(III) gives the concentration of total antimony, and antimony(V) is found from the difference between the results before and after reduction. Antimony in its different oxidation states can be determined in the range 0.04–0.7 mg l^?1 within an error of about 10%.     

Spectrophotometric determination of chromium(III, VI) by use of chromium(III, VI)-Chrome AzurolS-cetylpyridinium bromide-hydroxylamine hydrochloride-zinc(II) system

This paper shows that the sensitivity of the Cr(III, VI)—Chrome Azurol S (CAS)-cetylpyridinium bromide (CPB)—hydroxylamine hydrochloride system can be increased and the wavelength of maximum absorption slightly shifted by addition of zinc(II) and that the analytical data are practically identical for both Cr(III) and Cr(VI), indicating that under the conditions used both initial oxidation states of chromium yield the same final oxidation state, Cr(III). On the basis of the Cr(III, VI)—CAS—CPB—NH₂OH·HCl—Zn systems a new, highly sensitive and selective method for spectrophotometric determination of microamounts of Cr(III, VI) has been developed, with molar absorptivity of 1.27 × 10⁵ 1. mole⁻¹ . cm⁻¹ for the complex at 620 nm and linear calibration up to 0.4 μg/ml chromium. Various foreign ions do not interfere. The method can be applied to direct determination of chromium in steels.     

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…     

Redox titrations at millimolar concentration in n,n-dimethylformamide media

Potentiometric oxidation-reduction titrations in N,N-dimethylformamide (DMF) have been shown to be valid at millimolar concentrations of titrand. Forward and reverse titrations that involve the oxidants copper(II), chromium(VI), iron(III), and mercury(II) with the reductants titanium(III), cobalt(II), ascorbic acid, cysteine, and thiolactic acid have been examined. Some preliminary results of titanium(III) in DMF titrimetry in the determination of copper and iron in alloys are presented.     

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.     

The simple and rapid spectrophotometric determination of trace chromium(VI) after preconcentration as its colored complex on chitin

Preconcentration method with collection of metal complexes on a chitin has been applied to the spectrophotometric determination of chromium(VI) in water. The chromium(VI) is collected as its 1,5-diphenylcarbazide(DPC) complex on a column of chitin in the presence of dodecyl sulfate as counter-ion. The Cr-DPC complex retained on the chitin is eluted with a methanol-1 M acetic acid mixture (7:3, v/v), and the absorbance of the eluent is measured at 541 nm. Beer's law is obeyed over the concentration range of 0.05-0.6 mug of chromium(VI) in 1 ml of the eluent. The apparent molar absorptivity is 3.5x10(4) dm(3) mol(-1) cm(-1). The tolerance limits for Fe(III) is low, i.e. ten times that of chromium(VI), but some metal ions and common inorganic anions do not interfere in concentration range of 100-10 000 times that of chromium(VI). The present method can be applied to the determination of chromium(VI) in natural water samples.     

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%.     

Simultaneous flow injection determination of iron(III) and vanadium(V) and of iron(III) and chromium(VI) based on redox reactions

A flow injection analysis (FIA) method is presented for the simultaneous determinations of iron(III)-vanadium(V) and of iron(III)-chromium(VI) using a single spectrophotometric detector. In the presence of 1,10-phenanthroline (phen), iron(III) is easily reduced by vanadium(IV) to iron(II), followed by the formation of a red iron(II)-phen complex (lambda(max) = 510 nm), which shows a positive FIA peak at 510 nm corresponding to the concentration of iron(III). On the other hand, in the presence of diphosphate the reductions of vanadium(V) and/or chromium(VI) with iron(II) occur easily because the presence of diphosphate causes an increase in the reducing power of iron(II). In this case iron(II) is consumed during the reaction and a negative FIA peak at 510 nm corresponding to the concentration of vanadium(V) and/or chromium(VI) is obtained. The proposed method makes it possible to obtain both positive (for iron(III)) and negative (for vanadium(V) or chromium(VI)) FIA peaks with a single injection.     

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.     

Voltammetric determination of mercury(II) at a carbon paste electrode in aqueous solutions containing tetraphenylborate ion

The determination of mercury(II) ions can be achieved by monitoring the decrease in the oxidation peak of the tetraphenylborate ion in the presence of this metal ion at a carbon paste electrode. The reaction between mercury(II) and the tetraphenylborate ion results in the formation of diphenylmercury, thus providing the method with good selectivity over other metal ions. Using anodic stripping voltammetry in a neutral electrolyte, a linear dependence of the decrease of peak height was observed on increasing the mercury(II) concentration in the range 1 x 10(-6)-8 x 10(-9)M mercury(II). Zinc(II), cadmium(II), lead(II), nickel(II), cobalt(II), tin(II), potassium(I) and ammonium(I) ions did not interfere at a 1000-fold concentration excess. Iron(III) and chromium(III) did not interfere at a 250-fold and 50-fold concentration excess, respectively. Following masking procedures, copper(II), bismuth(III) and silver(I) did not interfere at a 100-fold concentration excess. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

Application of adsorptive stripping voltammetry (AdSV) for the analysis of trace metals in brine

Summary Routine analysis of brine for trace metals is important for safe and economical production in the alkali chloride electrolysis. As opposed to many spectroscopic techniques, trace metal determination by adsorptive stripping voltammetry (AdSV) is shown to be performed directly in brine. With minimal sample preparation chromium(VI), iron(III), nickel(II), cobalt(II), titanum(IV), manganese(II), molybdenum(VI) and vanadium(V) can be determined within minutes. The influence of parameters such as pH-value, supporting electrolyte solution, concentration of complexing reagents and possible interferents are investigated for optimal experimental conditions. Minimum detection limits are less than 5 ng/g for all trace metals except 1 ng/g for chromium(VI), cobalt(II) and molybdenium(VI) for 40 s adsorption periods with precisions of better than 7%. AdSV with linear or differential pulse scan is discussed.     

Flow potentiometric stripping analysis for mercury(II)

The optimum experimental conditions, with respect to sample and stripping solution composition, in computerised flow potentiometric stripping analysis for mercury(II) with a gold working electrode are described. When pre-electrolysis -was done in a sample to which ammonia and iodide had been added and stripping was done in an acidified bromide solution containing chromium(VI), a detection limit of 2 nM (0.4 μg kg^-1) was obtained after 90 s of pre-electrolysis, the dynamic range being almost three decades. Copper(II) interfered when present in a 1000-fold excess and silver(I) when present in a 5-fold excess over mercury(II).