Critical evaluation of three analytical techniques for the determination of chromium(VI) in soil extracts

Abstract

Three different analytical techniques [Ir5-diphenylcarbazide spectrophotometry, chelating ion-exchange chromatography (Chelex-IOO), and ion-pairing reversed-phase high-performance liquid chromatography (RP-HPLC) combined with electrothermal atomic absorption spectrometry (ETAAS)] were critically evaluated for the determination of CrV1 in soil extracts. Spectrophotometry was not applicable t o the analysis of most soil extract samples owing t o its high limit of detection (LOD = 30 ng cm-3), and the possibility of the instantaneous reduction of Crvl under the acidic conditions employed. A Chelex 100 column, although adequately sensitive (LOD = 1.5 ng cm-3), is inclined t o give higher results as inert and moderately labile Cr"l complexes partially passed through the resin together with CrVt. In addition, very small particles (€0.45 pm) carrying chromium can produce severe positive systematic errors. In order t o avoid this, filtration employing a 0.1 p m filter is recommended. Ion-pairing RP-HPLC was found t o be the most sensitive technique (LOD = 0.3 ng cm-3). It might also give high chromate results if negatively charged Cr1I1 complexes form ion pairs with tetrabutylammonium phosphate and their elution partially coincided with that of CrV1. Fulvate ligands showed this type o f interference. Reversed-phase HPLC is not suitable for analysis of extracts obtained from soils with freshly added tannery waste owing t o the effects of the undestroyed tannery waste matrix. This study showed that each method investigated was vulnerable t o some type of interference.

Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

“…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). Studies showed that interferences from organically complexed Cr(III) species were almost negligible in soil extracts when non-acidified DPC was used, and more significant with acidified DPC (Milacic et al, 1992 (Clesceri et al, 1998), as well as the removal of organic compounds from the samples (Mulaudzi et al, 2002), have been proposed. Very few methods for Cr determination are based on the formation of Cr(III) complexes in aqueous solution, and this is probably due to the slow reaction rate of the strongly hydrated Cr(III) ions.…”

“…One of the most used colorimetric methods for the Cr(VI) andyor total chromium determination is based on the reaction of Cr(VI) with diphenylcarbazide (DPC) (Lynch et al, 1984;Andrade et al, 1985;Milacic et al, 1992;Sule et al, 1996;Clesceri et al, 2002;Mulaudzi et al, 2002;Giusti et al, 2005). 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).…”

Determination of Cr(VI) in welding fumes by anion-exchange fast protein liquid chromatography with electrothermal atomic absorption spectrometric detection

“…After leaching, Cr(VI) was determined by ion chromatography or extraction with a liquid anion exchange solution of Amberlite LA 2/MIBK. Among different analytical techniques developed or modified in our laboratory for the determination of Cr(VI) in a variety of sample matrices [21,22,23,24] anion-exchange fast protein liquid chromatography (FPLC) with AAS detection offered simultaneous determination of Cr(III) complexes and Cr(VI) [25]. The technique was successfully applied in speciation of Cr in plant sap [25] and in the investigation of oxidation-reduction processes of trace amounts of Cr in highly alkaline lime-treated sewage sludge samples [26].…”

Preconcentration of Cr(III) and total Cr in waters for flame AAS in a flow-through electrochemical/sorption cell

“…Various separation techniques have been used for this purpose: electrodeposition [2], HPLC [3][4][5], sorption or ion exchange in a column [3,[6][7][8], selective evaporation in the graphite furnace [9]. The total Cr content can be determined after a reduction or oxidation procedure.…”