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The Chromium-Diphenylcarbazide Reaction1

Journal of the American Chemical Society (Impact Factor: 11.44). 10/1956; 78(19). DOI: 10.1021/ja01600a014
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    • "DPC forms a colored complex with Cr(VI) (dichromate) at acidic conditions [48], but not with Cr(III). However, DPC can be oxidized to diphenylcarbazone at alkaline conditions and in the presence of oxygen [48], which can form the same colored complex with Cr(III) as DPC forms with Cr(VI) [48]. DPC drops were applied on all unexposed leather samples. "
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    ABSTRACT: About 1-3% of the adult general population in Europe is allergic to chromium (Cr). The assessment of the potential release of Cr(III) and Cr(VI) from leather is hence important from a human health and environmental risk perspective. The Cr(VI) content in leather was recently restricted in the European Union. The aim of this study was to assess possible correlations between the bulk and surface chemistry of leather, released Cr(III) and Cr(VI), and capacities of co-released leather specific species to reduce and complex released Cr. Four differently tanned leathers were characterized by scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and the diphenylcarbazide colorimetric method. Their characteristics were compared with results on Cr(III) and Cr(VI) release into artificial sweat (ASW, pH <6.5) and phosphate buffer (PB, pH 7.5-8.0), measured by means of spectrophotometry and atomic absorption spectroscopy. Co-released leather-specific species were shown to reduce Cr(VI), both in ASW and in PB. Their reduction capacities correlated with findings of the surface content of Cr and of released Cr. Leather samples without this capacity, and with less aromatic surface groups visible by ATR-FTIR, revealed Cr(VI) both at the surface and in solution (PB).
    Journal of Hazardous Materials 09/2014; DOI:10.1016/j.jhazmat.2014.08.061 · 4.33 Impact Factor
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    • "The absorbance of the red – violet complex of unknown composition, formed at the pH range of 1.6 – 2.2, is read at 540 nm (Clesceri et al., 2002). Chromium (III) does not react with the DPC reagent (Pflaum et al., 1956). The sample acidification carried out before the DPC addition prevents the solubilization of Cr(III) species, the releasing of Cr(III) from complexes or colloidal particles, or even the increase of Cr(VI) reduction by organic compounds in the sample (Sule et al., 1996). "
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    ABSTRACT: A simple, fast and sensitive spectrophotometric method for the simultaneous determination of Cr(III) and Cr(VI) in effluents and contaminated waters using a UV-visible spectrophotometer, which operates with an advanced software for multicomponent analysis, is proposed. The method consists in the complexation of Cr (III) with EDTA and reaction of Cr(VI) with diphenylcarbazide (DPC). Variables, such as pH and colour stability time, were studied. The effect of concomitant ions on the simultaneous Cr(III) and Cr(VI) determination was also investigated. The sums of the chromium species concentrations obtained by the proposed method were compared with the total chromium concentrations found by electrothermal atomic absorption spectrometry. Recoveries of the chromium species between 75 and 136% were obtained for spiked samples. The linear working range for Cr(III) was 0.5-30 mg L−1, while for Cr(VI) was 0.005-0.30 mg L−1. The detection limits were 0.3 mg L−1 for Cr(III) and 0.003 mg L−1 for Cr(VI) while the quantification limits were 1.0 mg L−1 for Cr(III) and 0.01 mg L−1 for Cr(VI).
    Chemical Speciation and Bioavailability 07/2009; 21(3):153-160. DOI:10.3184/095422909X466095 · 0.38 Impact Factor
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    ABSTRACT: A method for sorption preconcentration of Cr(VI) from aqueous samples was developed using a polymer inclusion sorbent (PIS). The PIS used in this method was prepared by physical inclusion of Aliquat-336 in the matrix formed by cellulose triacetate and 2-nitrophenyl octyl ether. This sorbent was found to be stable, cost-effective, efficient for preconcentration of Cr(VI) present in the aqueous samples, and amenable to direct quantitative analysis of Cr(VI) held in it by neutron activation analysis and spectrophotometry. The quantifying of Cr(VI) in PIS by spectrophotometry was carried out by developing color directly on the PIS after reacting it with 1,5-diphenylcarbazide. The distinct color developed on the PIS even at very low concentrations of Cr(VI) suggests its possible use for field determination of Cr(VI). The composition of PIS was optimized to obtain maximum uptake of Cr(VI) without sacrificing uniformity in terms of thickness and distribution of ion-exchange sites, stability, and time required for quantitative sorption of Cr(VI) from aqueous samples. The Cr(VI) species held in the PIS, mainly HCrO4- and CrO4(2-), were found to vary as a function of pH of the aqueous samples from which Cr(VI) was preconcentrated. A close agreement was found in the abundances of Cr(VI) species held in the PIS with those reported in the literature for aqueous solutions at different pH. The variation of Cr(VI) species as a function of pH was found to have a significant impact on the tolerance to anions on the uptake of Cr(VI) in the PIS. The high selectivity of PIS toward Cr(VI) from aqueous solution at pH = 2 was explained on the basis of hydration of anions. The uptake of Cr(VI) was found to be fairly constant (88 +/- 3%) up to nearly complete exchange of counterions present in the PIS. The method developed in the present work was successfully used for the preconcentration of Cr(VI) from tap water and seawater samples containing low levels of Cr(VI).
    Analytical Chemistry 09/2002; 74(16):4204-12. DOI:10.1021/ac025640u · 5.83 Impact Factor
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