Sorption of chromium(VI) and chromium(III) on aluminium hydroxide

Factors that influence the sorption of Cr(VI) and Cr(III) on aluminium hydroxide were investigated. The sorption of chromates decreases as the pH of the suspension increases. The mechanism of CrO ₄ ^2– sorption was interpreted in terms of reactions between chromates and –OH and/or H₂O groups at the hydroxide/liquid interface. It has been shown that chromates are more tightly sorbed on aluminium hydroxide compared to other anions, e.g. chlorides. On the other hand, specifically absorbed anions, such as molybdates, compete strongly with chromates for the sorption sites. The sorption of chromium(III) increases with the pH of the suspension. Also, the sorption of chromium(III) is suppressed in the presence of citrate ions. The best conditions for the fixation of Cr(VI) and Cr(III) by aluminium hydroxide are presented.     

Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

Determination of chromium(III) and total chromium in marine waters

The development of an analytical technique is described which may be used to determine chromium, chromium(III) and chromium(VI) in estuarine and coastal waters. The method is based on selective micro-solvent extraction with subsequent GFAAS. The technique has been applied in a major North Sea estuary. The results obtained confirm that thermodynamic factors alone cannot be relied upon to describe the form of chromium in estuaries. Kinetic factors appear to have a strong influence over speciation and lead to the persistence of Cr(III) species in environments where Cr(VI) would be expected to be present.     

Cloud point extraction combined with graphite furnace atomic absorption spectrometry for the determination of chromium species and their distribution in cigarette and cigarette ash

In this article, the contents and distribution of total chromium, Cr(III) and Cr(VI) in various cigarettes and cigarette ashes were determined by using a cloud point extraction (CPE) separation/preconcentration combined with graphite furnace atomic absorption spectrometric (GFAAS) detection. Different extraction reagents, such as tetramethylammonium hydroxide (TMAH), Na₂HPO₄, Na₂CO₃/NaOH, NaOH and H₂O, were tested for the extraction of Cr species, and the extraction efficiency was estimated. The experimental results showed that TMAH was the most efficient extraction reagent for the analyte in cigarette samples. By using the established method, the total chromium, Cr(III) and Cr(VI) in various cigarettes and cigarette ashes were determined and their distribution was studied. It was found that Cr(III) is a main species in cigarettes, but that it can be partly oxidized to Cr(VI) during smoking.     

Thermolyse de mélanges de chromates et d'oxalates de métaux alcalino-terreux II. Composés du magnésium

The thermolysis of mixtures of chromates and oxalates of magnesium has been studied combining thermal analysis and electron paramagnetic resonance. It is found that both the reduction of Cr(VI) to Cr(III) and that of Cr(VI) to Cr(V) are spontaneous and occur at about 600 and 250°C, respectively, under vacuum. Highly dispersed Cr(V) species are present after activation below 400°C while dispersed Cr(II) species, either as Cr₂O₃ or as Cr(III) in solid solution in the MgO lattice, are observed above 350 and 550°C, respectively. CO evolved during the decomposition of the oxalate is found to play a major role in the reduction of Cr(V) in Cr(III). Contrarily to the observation on the Ba and Sr homologues, no effect of the carbonate has been found.     

Method Development for the Speciation of Chromium in River and Industrial Wastewater Using GFAAS

A simple, sensitive and inexpensive method for the speciation of Cr(VI) and Cr(III) in river and industrial wastewater was developed, optimized and validated. Samples were collected, filtered and then chromium species were determined in the filtrate. In the filtrate, total Cr was determined directly by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). A portion of the filtered sample was buffered to pH 6.4, extracted with Amberlite LA-2/MIBK and finally Cr(VI) was determined in the organic extract and Cr(III) in the aqueous phase using GFAAS. The method was evaluated by analysis of the certified reference material, CRM 544, and good accuracy was obtained. The limit of detection for Cr(VI) and Cr(tot)/Cr(III) was found to be 0.30 and 0.08 µg L⁻¹, respectively, and a precision expressed as relative standard deviation of better than 11% was achieved for nine replicates. A number of water samples from the Tinishu Akaki River, Ethiopia, and wastewater samples from a chemical plant in Germany, were analysed. In addition to the GFAAS method, Cr(tot) was also determined using ICP-MS (in CRM 544, lyophilized water, and Tinishu Akaki River water samples) and Cr(tot) and Cr(VI) using UV-VIS spectrophotometry (in CRM 544 and industrial wastewater samples). Good agreement between the different methods was found.     

Flow-injection configurations for chromium speciation with a single spectrophotometric detector

The simultaneous or sequential determination of chromium(VI) and total chromium in water by flow injection analysis, using different configurations with a double- or single-beam spectrophotometer as detector, is investigated. The method is based on reaction between chromium(VI) and 1,5-diphenylcarbazide. Chromium(III) and (VI) are distinguished by using two carrier streams, one of which contains cerium(IV) to oxidize chromium(III) to chromium(VI). The determination range is 0.2–10.0 μg Cr ml^?1; the r.s.d. is 0.8% for 1 μg Cr. The sampling frequency is 40 h^?1. A wide study of interferences is reported.     

Determination of trace metals and speciation of chromium ions in atmospheric precipitation by ICP-AES and GFAAS

Sampling and analytical techniques used for determining trace metal concentrations in atmospheric precipitation waters collected in Hungary are presented. The results of the analyses are briefly discussed and special attention is devoted to chromium speciation. For the preconcentration of the trace metals a chelating cellulose, iminodiacetic acid ethylcellulose (IDAEC) microcolumn was used in a flow-injected system. Cd, Co, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn were determined by ICP-AES. In precipitation water the concentrations of the trace elements were in the 0.1-50 mug/l. range. The two forms of chromium, Cr(III) and Cr(VI) were separated using IDAEC and the anion exchanger diethylamine ethylcellulose, respectively. Cr was determined by GFAAS. In atmospheric precipitation the concentration of Cr(III) was in the range of 0.1-0.4 mug/l. while that of Cr(VI) in the range of 0.04-0.1 mug/l.     

Speciation of Cr(III) and Cr(VI) ions using a β-cyclodextrin-crosslinked polymer micro-column and graphite furnace atomic absorption spectrometry

A sensitive and selective method for the speciation of Cr(III) and Cr(VI) in water samples was developed. It is based on the selective binding of the complex formed between Cr(III) and 4-(2-pyridylazo)resorcinol adsorbed on a cross-linked polymer modified with β-cyclodextrin and placed in a micro-column. Graphite furnace atomic absorption spectrometry (GFAAS) was used to quantify chromium. Cr(VI) ion is not adsorbed but remains in the aqueous sample phase. Thus, an in-situ separation of Cr(VI) and Cr(III) is accomplished. The concentration of Cr (VI) was calculated by subtracting the value for Cr(III) from that for total chromium. Under optimum conditions, the limit of detection of Cr(III) is 0.056 μg L^?1, and the linear range is from 2.0 to 160.0 μg L^?1. The relative standard deviation is 2.5% (n?=?3, at 30.0 μg L^?1). The preconcentration factor is 25. The method was applied to the speciation of chromium in water samples, and recoveries in spiked real samples range from 101.9% to 104.5%. A reference water sample (GBW(E)080642) also was analyzed, and the results were in good agreement with the certified values.

A two-step extraction method for differentiating chromium species in water

The hexavalent Cr species Cr(VI) in natural waters can be quantitatively extracted by diethyldithiocarbamate (DDTC) in the pH range 4.0–4.5 into chloroform, followed by back-extraction into a Hg(II) solution for graphite furnace atomic absorption spectrometry (GFAAS). The trivalent Cr(III) species can be oxidized to Cr(VI) by KMnO₄ and then extracted by the DDTC-Hg(II) procedure. The proposed two-step extraction method combined with GFAAS is suitable for Cr speciation studies in natural water systems.     

Stability of fluoroquinolone antibiotics in river water samples and in octadecyl silica solid-phase extraction cartridges

Airborne particulate matter has been sampled at a location close to a metallurgical plant in North-Rhine-Westphalia, Germany, and first results on the chromium(VI) content in the collected dust are presented. A special procedure using a scrubber as sampling device was used to preserve Cr(VI) during the sampling procedure. The scrubber solution which consisted of 0.1 mol L^–1 TRIS-buffer solution was adjusted to a slightly alkaline pH of 8.6 to reduce the oxidation potential of Cr(VI) and to avoid possible oxidation of Cr(III) to Cr(VI), for example by oxygen (or ozone at ambient concentrations). After sampling Cr(VI) was pre-concentrated on an anion-exchange material and eluted with aqueous 0.6 mol L^–1 sodium perchlorate solution. After elution, a species-selective complex of Cr(VI) with diphenylcarbazide (DPC) was prepared; this was extracted into n-hexanol and quantified by UV–visible spectrophotometry. A detection limit of 0.9 ng m^–3 for Cr(VI) in ambient aerosols can be achieved with this method.     

The effect of Cr(III)-organic complexes on the determination of inorganic chromium species in groundwater by ammonium pyrrolidinedithiocarbamate–methylisobutylketone extraction procedure

Groundwater samples collected from a tannery contaminated area were analyzed for chromium species with the objective of investigating the interference of Cr(III)-organic complexes in the determination of Cr(VI) using APDC–MIBK extraction procedure. The contribution of Cr(III), Cr(VI) and Cr(III)-organic complexes towards total chromium ranged between 2 and 61%, 27 and 86%, and, 6 and 23%, respectively. The Cr(III)-organic complexes were not extractable by APDC–MIBK, however, HNO₃ digestion released the organic bound Cr(III). Interference of organic bound Cr(III) in Cr(VI) determination due to MIBK soluble Cr(III) was not observed. Significant difference between total dissolved chromium determined after appropriate digestion procedure, and the sum of dissolved Cr(III) and Cr(VI) determined indicates the presence of the Cr(III)-organic complexes. MIBK extraction of samples without APDC is an useful way to check the extractability of organic bound Cr(III). The presence of soluble Cr(III)-organic complexes thus add complexity to chromium speciation analysis by APDC–MIBK procedure.     

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).     

Preconcentration method on modified silica fiber for chromium speciation

A new method involving pre-concentration on modified silica fiber is described for the speciation of chromium(III) [Cr(III)] and chromium(VI) [Cr(VI)] in aqueous media. This method is based on the different chelating behavior of Cr(III) and Cr(VI) with morpholine-4-carbodithioate (MDTC). Both complexes are extracted on silica fiber modified by sol-gel technology by using 3-aminopropyltriethoxysilane (APS) as a precursor. All extracted samples are directly injected into an high-performance liquid chromatography injector for the simultaneous determination of Cr(III) and Cr(VI). Cr(VI) forms two different complexes, and Cr(III) forms a single complex with MDTC. Therefore, the concentration of Cr(VI) is determined directly from the peak area obtained at 5.4 min; whereas, the assay of Cr(III) is based on subtracting the peak area of Cr(VI) from the total peak area obtained at 4.3 min. Under the optimized conditions, the limits of detection for Cr(III) and Cr(VI) are found to be 0.7 ng/mL and 0.2 ng/mL, respectively.     

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.     

Chromium speciation in natural waters using serially connected supported liquid membranes

A supported liquid membrane (SLM) method for the speciation of chromium has been developed. The method is based on selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two serially connected SLM units. Methyltricaprylammonium chloride (Aliquat) and di-(2-ethylhexyl) phosphoric acid (DEHPA), respectively were used as the selective extractants in the membrane liquid. Graphite furnace atomic absorption spectrometry (GFAAS) was utilised for final determination. Optimised conditions for the DEHPA membrane were, sample solution at pH 3, acceptor solution 0.1 M HNO₃ and 10% w/w carrier in kerosene. The corresponding values for the Aliquat membrane were pH 7, 0.75 M HNO₃ and 6% w/w carrier in di-n-hexylether. This gave extraction efficiencies for Cr(III) and Cr(VI) of 90 and 40%, respectively. The method was used to measure the concentration of Cr III and Cr VI in surface water from an abandoned tannery site. Storage experiments at different pH showed that preservation at neutral pH gave almost constant values over a period of one month. At acidic pH (pH=3.0) the concentration of Cr(VI) decreased rapidly while the concentration of Cr(III) increased. The detection limit, expressed as three times the standard deviation of enriched blank samples was 0.01 μg l⁻¹.     

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.     

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 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.     

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%.