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 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%.     

Rapid separation and determination of chromium

Chromium(III) is oxidized to chromium(VI) at room temperature or by conventional persulphate oxidation. The chromium(VI) is separated from other metal ions by retention on a small anion-exchange column, and then eluted with a perchlorate solution and measured spectrophotometrically with a flow-through cell. The method is rapid, selective and amenable to automation.     

Selective separation and determination of dissolved chromium species in natural waters by atomic absorption spectrometry

A procedure for determining the concentrations of dissolved chromium species in natural waters is described. Chromium(III) and chromium(VI), separated by co-precipitation with hydrated iron(III) oxide, and total dissolved chromium are determined separately by conversion to chromium(VI), extraction with APDC into MIBK and determination by a.a.s. The detection limit is 40 ng l^?1 Cr. The dissolved chromium not amenable to separation and direct extraction is calculated by difference. In the waters investigated, total concentrations were relatively high (1–5 μg l^?1) with Cr(VI) the predominant species in all areas sampled with one exception, where organically bound chromium was the major species.     

Determination of tributyltin in toluene extract from sea water by graphite furnace atomic absorption spectrometry with a new matrix modifier

A new matrix modifier composed of calcium and chromium[VI] was proposed for the determination of tributyltin (TBT) in toluene extract from sea water containing sediment by graphite furnace atomic absorption spectrometry (GFAAS). Fourteen inorganic and organic compounds (barium, calcium, chromium[VI], lanthanum, magnesium, nickel, palladium, strontium, calcium-chromium[VI], calcium-strontium, nickel isocaprylate, 5%-, 10%-aqueous solution of ascorbic acid and toluene-saturated solution of ascorbic acid) as a matrix modifier were comparatively studied and a matrix modifier composed from 5 microg of calcium and 1 microg of chromium[VI] was found to give the best performance. The interference effects of co-existing elements in sea water containing sediment (aluminium, iron, magnesium, sodium and strontium) were studied. TBT in eight toluene extracts was determined by GFAAS with the proposed matrix modifier. The relative standard deviation was 3.0% for 63 ng ml(-1) of TBT (n = 11). The recoveries were 88-104%. The characteristic mass was 7 pg. The linearity range was 0-250 ng mg(-1).     

A simultaneous EDTA-metric determination of calcium and magnesium with antipyrylazo III and thymolphthalexon

The simultaneous determination of calcium and magnesium in natural materials (limestone and dolomite) can be made by EDTA-metric titration at pH 13.0–13.3 and 10.2–10.5 indicated by antipyrylazo III (diantipyrylaxo; 3,6-diantipyrylazo-4,5-dihydroxy-2, 7-naphthalenedisulfonic acid) and thymolphthalexon (3′,3″-bis[bis(carboxymethyl)aminomethyl]-thymolphthalein), respectively. Sodium cyanide and triethanolamine are used as masking reagents, hydroxylamine hydrochloride is the bleaching (reducing) reagent to remove the antipyrylazo III color for the subsequent magnesium titration. Antipyrylazo III is also a convenient indicator for EDTA-metric determination of copper(II) in aqueous ammonia.     

Determination of calcium and magnesium in limestone and dolomite by enthalpimetric flow-injection analysis

A flow-enthalpimetric method for the determination of calcium and magnesium in limestone and dolomite is described. Calcium is determined by measuring the heat evolved from the substitution reaction with Mg-EDTA. The amount of magnesium is calculated from the calcium content and the enthalpimetric signal for the reaction of the sample solution with disodium-EDTA, which gives the total concentration of calcium and magnesium. Analysis of reference materials and other samples indicates an error not exceeding 0.3% of CaO and MgO, and a sampling rate of 100 samples per hour.     

Speciation of chromium in mineral waters and salinas by solid-phase extraction and graphite furnace atomic absorption spectrometry

A simple GF-AAS method for speciation analysis of chromium in mineral waters and salinas was developed. Cr(VI) species were separated from Cr(III) by solid-phase extraction with APDC (ammonium pyrrolidinedithiocarbamate). The APDC complexes were formed in the sample solution under proper conditions, adsorbed on Diaion HP-2MG resin and the resin was separated from the sample. After elution with concentrated nitric acid Cr(VI) was determined by GF-AAS. Total chromium was determined by GF-AAS directly in the sample and Cr(III) concentration was calculated as the difference between those results.

The detection limit of the method defined as 3 s of background variation was 0.03 μg l⁻¹ for Cr(VI) and 0.3 μg l⁻¹ for total chromium. RSD for Cr(VI) determination at the concentration of 0.14 μg l⁻¹ was 9%, and for total chromium at the concentration of 5.6 μg l⁻¹ was 5%. The recovery of Cr(VI) was in the range of 94–100%, dependently on type of the sample.

The investigation of recovery of the spiked Cr(VI) showed that at concentration levels near 1 μg l⁻¹ and lower recovery may be reduced significantly even by pure reagents that seem to be free from any reductants.     

Chromium speciation using an automated liquid handling system with inductively coupled plasma - mass spectrometric detection

The speciation of inorganic chromium in environmental samples is required for accurate assessment of pollution levels. Of the two chromium oxidation states, Cr (VI) is a known carcinogen, while Cr (III) is an essential element. Total chromium measurement cannot be used to determine actual environmental impact due to the considerable difference in toxicity of the two elemental forms. An automated liquid handling system, the PrepLab™, can be used with an inductively coupled plasma-mass spectrometer (ICP-MS) to quantify Cr (III) and Cr (VI) in liquid samples. An autosampler is used to introduce discrete sample volumes into a solid-phase chelation resin column. The Cr (III) and Cr (VI) species are separated and are introduced on-line into the VG PlasmaQuad 3 ICP-MS for detection. The chromatographic data are collected in time resolved analysis mode with the capability of simultaneous multiple-isotopic detection.     

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.     

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.     

Extractions with long-chain amines-VIII Colorimetric determination of chromium(VI) with diphenylcarbazide

Traces of chromium(VI) are extracted from sulphuric acid solution into a chloroform solution of trioctylmethylammonium chloride. After the addition of solid diphenylcarbazide to the separated organic phase, a red colour is developed and is measured spectrophotometrically at 550 nm. A great number of common metals, including iron and copper, do not interfere when present in ratios up to at least 1:40,000 (chromium: metal).     

Anion exchange separation of chromium and molybdenum from iron,vanadium, uranium and other elements in malonic acid solution

Summary Anion-exchange behaviour of chromium (III) and molybdenum (VI) was studied in malonate media. They form anionic complexes with malonic acid at pH 5.6. Various eluants, such as mineral acids and their salts were tested and a selectivity scale evolved. Cr and Mo were separated from Tl(I), alkali and alkaline earth elements by selective sorption and from Co(II), Ni(II), Mn(II), Zn(II) and Cd(II) by selective washing with water. They were separated from many other elements by selective elution. The sequential separation of Fe(III) V(IV), Cr(III), Mo(VI) and U(VI) was significant.     

贵州瓮福地区磷尾矿中钙、镁、磷的赋存状态测定

应用化学组分分析、X射线衍射分析、扫描电子显微镜及X射线能谱法等多种方法对贵州省瓮福地区磷尾矿中钙、镁及磷的赋存状态作了分析和研究。结果表明:①选自该矿区的磷尾矿为高镁(wMgO17.26%～17.65%),高钙(wCaO34.11%～34.56%),低磷(wP2O55.30%～5.69%)的固体矿物;②尾矿中镁主要以白云石形式存在,并有少量以磷酸盐和硅酸盐形式存在;钙主要也以白云石形式存在,加上少量以方解石和磷酸盐形式存在;磷主要以磷灰石形式存在,有少量存在于铁氧化物及独居石、磷钇矿中。     

Étude de l’élimination du Cr(VI) par l’oxyde mixte obtenu par calcination de l’hydroxyde double lamellaire MgAl

A magnesium aluminium hydrotalcite-like compound (HT) containing carbonate anions in the interlayer space and with a final Mg/Al ratio of 2 was synthesized by the co-precipitation method. The obtained material was characterized by powder X-ray diffraction (XRD), Fourier-Transform–Infrared spectroscopy (FT–IR), thermal analysis (ATG/ATD), and surface area measurements (BET). The interaction of the clay with Cr(VI) has been studied by ultraviolet–visible (UV–vis) spectroscopy. The calcined hydrotalcite (HT-C) showed the highest capacity of removal of chromium ions, and their sorption capacities for Cr(VI) are 4.85 mmol/g. The effect of various parameters on the preparation conditions for the removal of chromium, such as the contact time, the amount of sorbent, the initial concentration of Cr(VI), and the pH values of aqueous solution were also investigated to identify their influence on Cr(VI) sorption. The characterization of the calcined hydrotalcite (HT-C) after interaction with Cr(VI) ions by FT–IR spectroscopy showed that Cr(VI) was adsorbed and intercalated by the solid.     

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.     

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.     

Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its diphenylcarbazide complex on a mixed bed adsorbent (acid activated montmorillonite-silica gel) column

A novel approach has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its diphenylcarbazide complex on a mixture of acid activated montmorillonite (AAM)-silica gel column. The effect of various parameters such as acidity, stability of the column, sample volume, interfering ions, etc., were studied in detail. The adsorbed complex could be easily eluted using polyethylene glycol-sulfuric acid mixture and the concentration of chromium has been determined using visible spectrophotometry. The calibration graph was linear in the range 0-1microgmL(-1) chromium(VI) with a detection limit of 6microgL(-1). A highest preconcentration factor of 25 could be obtained for 250mL sample volume using glass wool as support for the mixed bed adsorbent. Chromium(VI) could be effectively separated from other ions such as nickel, copper, zinc, chloride, sulfate, nitrate, etc., and the method has been successfully applied to study the recovery of chromium in electroplating waste water and spiked water samples.     

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.     

Speciation of chromium in sea water

Dissolved chromium(III) and (VI) are coprecipitated separately from sea water, and chromium in the precipitates and particulate matter is determined by thin-film x-ray fluorescence spectrometry. In combination with an ultraviolet irradiation procedure whch releases bound metals, the method provides information about the speciation of chromium in near-shore surface sea water. The ratios of labile Cr(III)/(IIO+VI) generally lie in a narrow range (0.4–0.5) as do the sums of labile Cr(III) and (VI) concentrations (0.3–0.6 μg l^?1). Bound chromium is variable (0–3 μg l^?1) and constitutes from 0 to 90% of total dissolved chromium. Acidification of the samples in the traditional manner for trace metal determination is shown to alter the proportion of Cr(III) to Cr(VI).