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A procedure for the determination of chromium is described based on synergistic pre-concentration of the chromate anion at a carbon paste electrode modified in situ with quarternary ammonium salts such as 1-ethoxycarbonylpentadecyltrimethylammonium bromide (Septonex((R))), cetyltrimethylammonium bromide (CTAB) or cetylpyridinium bromide (CPB). The proper electrochemical detection utilises the reduction Cr(VI) --> Cr(III) performed in the differential pulse cathodic voltammetric mode. In discussion, considerable attention has been paid to the accumulation mechanism at the carbon paste electrode in the presence of surfactants. Furthermore, after optimising the corresponding experimental conditions (0.1-0.3M HCl + 0.1M NaCl as the supporting electrolyte, 2.5-25muM as the total concentration of modifier, pre-concentration at +0.7V versus Ag/AgCl and the stripping from +0.7 to -0.4V), the analytical performance of the method has been evaluated. The signal of interest was reproducible within +/-8% and proportional to the concentration in a range of 0.5-50muM CrO(4)(2-), with a limit of detection (S/N = 3:1) of about 5x10(-8)M CrO(4)(2-) (with accumulation for 300s). Interference studies were focused mainly on the species capable of forming ion-pairs with the modifier; i.e., TlCl(4)(-), AuCl(4)(-), PdCl(4)(2-), PtCl(6)(2-), VO(4)(3-), MnO(4)(-) and I(-). Practical applicability of the method was tested on model solutions via the recovery rates (typically 90-110%) or using selected certified reference materials (tea, bush leaves, clover) and two samples of black tea when the respective results were compared to those obtained by the reference determinations with ICP-AES.
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PMID:A study on the determination of chromium as chromate at a carbon paste electrode modified with surfactants. 1896 79

A new functionalized calix[6]crown hydroxamic acid is reported for the speciation, liquid-liquid extraction, sequential separation and trace determination of Cr(III), Mo(VI) and W(VI). Chromium(III), molybdenum(VI) and tungsten(VI) are extracted at pH 4.5, 1.5M HCl and 6.0M HCl, respectively with calixcrown hydroxamic acid (37,38,39,40,41,42-hexahydroxy7,25,31-calix[6]crown hydroxamic acid) in chloroform in presence of large number of cations and anions. The extraction mechanism is investigated. The various extraction parameters, appropriate pH/M HCl, choice of solvent, effect of the reagent concentration, temperature and distribution constant have been studied. The speciation, preconcentration and kinetic of transport has been investigated. The maximum transport is observed 35, 45 and 30min for chromium(III), molybdenum(VI) and tungsten(IV), respectively. For trace determination the extracts were directly inserted into the plasma for inductively coupled plasma atomic emission spectrometry, ICP-AES, measurements of chromium, molybdenum and tungsten which increase the sensitivity by 30-fold, with detection limits of 3ngml(-1). The method is applied for the determination of chromium, molybdenum and tungsten in high purity grade ores, biological and environmental samples. The chromium was recovered from the effluent of electroplating industries.
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PMID:Speciation, liquid-liquid extraction, sequential separation, preconcentration, transport and ICP-AES determination of Cr(III), Mo(VI) and W(VI) with calix-crown hydroxamic acid in high purity grade materials and environmental samples. 1897 Jan 44

On-line preconcentration system for the selective, sensitive and simultaneous determination of chromium species was investigated. Dual mini-columns containing chelating resin were utilized for the speciation and preconcentration of Cr(III) and Cr(VI) in water samples. In this system, Cr(III) was collected on first column packed with iminodiacetate resin. Cr(VI) in the effluent from the first column was reduced to Cr(III), which was collected on the second column packed with iminodiacetate resin. Hydroxyammonium chloride was examined as a potential reducing agent for Cr(VI) to Cr(III). The effects of pH, sample flow rate, column length, and interfering ions on the recoveries of Cr(III) were carefully studied. Five millilitres of a sample solution was introduced into the system. The collected species were then sequentially washed by 1M ammonium acetate, eluted by 2M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15mugl(-1), respectively. The total analysis time was about 9.4min. The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results.
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PMID:On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry. 1897 Mar 34

A sensitive method for the determination of chromium ion(VI) in complex matrices such as crude oil and sludge is presented based on the decreasing effect of Cr(VI) on cathodic adsorptive stripping peak height of Cu-adenine complex. Under the optimum experimental conditions (pH 7.5 Britton-Robinson buffer, 5x10(-5)M copper, 8x10(-6)M adenine and accumulation potential -250mV versus Ag/AgCl), a linear decrease of the peak current of Cu-adenine was observed, when the chromium(VI) concentration was increased from 5mugL(-1) to 120mugL(-1). Detection limit of 2mugL(-1) was achieved for 120s accumulation time. The relative standard deviations (R.S.D., %) were 1.8% and 4% for chromium(VI) concentrations of 18mugL(-1) and 100mugL(-1), respectively. The method was applied to the determination of chromium(VI) in the presence of high levels of chromium(III), in various real samples such as crude oil, crude oil tank button sludge, waste water and tap water samples. Effects of foreign ions and surfactants on the voltammetric peak and the influences of instrumental and analytical parameters were investigated in detail. The accuracy of the results was checked by ICP and/or AA.
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PMID:Indirect determination of hexavalent chromium ion in complex matrices by adsorptive stripping voltammetry at a mercury electrode. 1897 Apr 39

Water-soluble heavy metal salts injure health when they leach into water supplies. It is important that students who may later be employed in industries generating aqueous solutions of such salts are aware of the methods that can be used to recover the metal salt or transform it to non-health threatening products. The research was in the management of small quantities of hazardous wastes, such as are generated in school, college, and university teaching laboratories; in research laboratories; in industrial quality control and testing laboratories; and in small industries. Methods for the recovery of silver, nickel, and cobalt salts from relatively small volumes of aqueous solutions of their soluble salts were developed and tested. Where it was not practical to recover the metal salt, the practice has been to convert it to a water-insoluble salt, often the sulfide. This requires the use of highly toxic reagents. It was found that a number of heavy metal salts can be precipitated as the silicates, returning them to the form in which they are found in the natural ore. These salts show similar solubility properties to the sulfides in neutral, acidic, and basic aqueous solutions. The work has determined the conditions, quantities, and solution acidity that result in the most effective precipitation of the heavy metal salt. The concentration of the metal ions remaining in solution was measured by AA and ICP spectrometry. Specific methods have been developed for the conversion of salts of mercury and chromium to nonsoluble products.
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PMID:Protecting health. 1899 43

The concentrations of cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead, and zinc were determined by ICP-AES in muscles and livers of eight fish species sampled from the Aegean and Mediterranean seas of Turkey. Iron showed the highest levels, followed by Zinc in examined tissues of all fish species. Metal concentrations in edible parts of fish species were 0.03-0.37 mg kg(-1) for cadmium, 0.02-0.42 mg kg(-1) for cobalt, 0.15-1.78 mg kg(-1) for chromium, 0.17-1.11 mg kg(-1) for copper, 11.0-33.4 mg kg(-1) for iron, 0.02-0.89 mg kg(-1) for manganese, 0.22-4.03 mg kg(-1) for nickel, 0.22-0.64 mg kg(-1) for lead, and 2.88-10.9 mg kg(-1) for zinc, respectively. All metal concentrations in livers were higher than those in muscles. In some stations, cadmium, chromium, cobalt, and lead concentrations in both muscles and livers of the examined species were higher than permissible safety levels for human uses.
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PMID:Metal concentrations in eight fish species from Aegean and Mediterranean Seas. 1906 6

The concentrations of chromium (III) and (VI) in fly ash from nine Australian coal fired power stations were determined. Cr(VI) was completely leached by extraction with 0.01 M NaOH solution and the concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). This was confirmed by determining Cr(III) and Cr(VI) in the extracts of fly ash that had been spiked with chromium salts. These analytical measurements were done using a combination of ion-exchange chromatography and ICP-AES. The elutant was 0.05 M HNO(3) containing 0.5%-CH(3)OH. When the column was operated at a flow rate of 1.2 ml min(-1) and samples were injected by use of a sample loop with a volume of 100 microl, Cr(III) and Cr(VI) in sample solution was exclusively separated within approximately 10 min. The detection limits (3sigma) were 5 ng for Cr(III) (0.050 mg l(-1)) and 9 ng for Cr(VI) (0.090 mg l(-1)), respectively. A relative standard deviation of 1.9% (n=6) was obtained for the determination by IC-ICP-AES of 0.25 mg l(-1) Cr(III) and Cr(VI).
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PMID:Speciation of chromium in Australian fly ash. 1907 66

When inductively coupled plasma mass spectrometry (ICP-MS) is used for the detection of (52)Cr (83.8%) species in ion chromatography (IC), interference from polyatomic ions such as (40)Ar(12)C(+) and (35)Cl(16)O(1)H(+), often occurs due to their mass at m/z 52. To address the issue, an octopole reaction system (ORS) in ICP-MS, including He and H(2) modes, was used to determine whether the background and interference from polyatomic ions could be reduced in the detection of (52)Cr. Compared to standard mode, the polyatomic ions were reduced by either He or H(2); for example, more than 97 and 98% of (35)Cl was removed using a He and H(2) tune, respectively. However, the detection sensitivity for (52)Cr was decreased, for example, the sensitivity was 27.95 and 67.02% of the standard mode for Cr(EDTA)(2)(-)using a He and H(2) tune, respectively. The H(2) tune is recommended for the detection of (52)Cr at a flow rate of 2.0mL/min with detection limits in the range of 0.2-0.4mug/L. The developed method was used to measure chromium speciation in waters containing high concentration of chloride.
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PMID:Removal of interferences in the speciation of chromium using an octopole reaction system in ion chromatography with inductively coupled plasma mass spectrometry. 1907 26

Elemental speciation is becoming a common analytical procedure for geochemical investigations. The various redox species of environmentally relevant metals can have vastly different biogeochemical properties, including sorption, solubility, bioavailability, and toxicity. The use of high performance liquid chromatography (HPLC) coupled to elemental specific detectors, such as inductively coupled plasma mass spectrometry (ICP-MS), has become one of the most important speciation methods employed. This is due to the separation versatility of HPLC and the sensitive and selective detection capabilities of ICP-MS. The current study compares standard mode ICP-MS to recently developed reaction cell (RC) ICP-MS, which has the ability to remove or reduce many common polyatomic interferences that can limit the ability of ICP-MS to quantitate certain analytes in complex matrices. Determination of chromium and selenium redox species is achieved using ion-exchange chromatography with elemental detection by standard and RC-ICP-MS, using various chromium and selenium isotopes. In this study, method performance and detection limits for the various permutations of the method (isotope monitored or ICP-MS detection mode) were found to be comparable and generally less than 1 microg L(-1). The method was tested on synthetic laboratory samples, surface water, groundwater, and municipal tap water matrices.
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PMID:Comparison of standard and reaction cell inductively coupled plasma mass spectrometry in the determination of chromium and selenium species by HPLC-ICP-MS. 1910 Aug 79

Chitosan resin possessing the 4-hydroxyphthalic acid moiety (CCTS-HPA resin) was synthesized. This resin could adsorb chromium(VI) at pH 3 to 5, whereas chromium(III) could not be retained in the acidic region. The CCTS-HPA resin was used for collecting chromium(VI), and ME-03 resin was used for collecting chromium(III) before their measurement by ICP-AES measurement. Both resins were packed in mini-columns and installed serially in a laboratory-assembled automated pretreatment system (Auto-Pret System). The system provides a highly sensitive and fully automated procedure for the speciation of chromium(III) and chromium(VI). The proposed system was successfully applied to speciation of chromium(III) and chromium(VI) using 5 ml of water samples. The detection limits (S/N = 3) of chromium(III) and chromium(VI) were 0.06 and 0.04 microg l(-1), respectively, along with an analysis time of 7 min 45 s for both chromium species. The lowest determinable concentrations for both chromium species were about 0.5 microg l(-1), which was enough for the speciation of chromium in water samples.
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PMID:Automated pretreatment system for the speciation of Cr(III) and Cr(VI) using dual mini-columns packed with newly synthesized chitosan resin and ME-03 resin. 1913 72


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