Methodology for the speciation of cr(III) and cr(VI) in leaf powders using the sulfate form of dowex-1 after microwave extraction and ICP-OES detection

Abstract

The speciation of chromium (Cr) in different leaf samples from black tea, green tea, spinach, the Ceiba pentandra and Croton escabiosis fruit trees, and one custard apple tree (Annona reticulata) is reported by using offline separation and ICP-OES detection. The species of Cr are extracted using a solution containing 0.1 M EDTA, 1% tetrabutyl ammonium bromide (TBAB), and a little HF in a domestic microwave oven for 1 minute. Optimization of the methodology for the extraction of the Cr species from dried leaf powders and separation of Cr(VI) from the extract were studied. The determination of the separated Cr(VI) and total Cr in the extracts and also total Cr after total digestion was carried out using ICP-OES. Recovery of the extracted Cr was 97-103%, calculated with respect to the total Cr concentration obtained after complete dissolution. Separation of Cr(VI) from the extracts was carried out using anion exchange chromatography with a sulfate form of Dowex-1 at pH 4.5. The recovery of Cr(VI) was found at 98–101% with an RSD of 5–6 %. The limits of detection for Cr(III) and Cr(VI) were 18 and 21 ng g-1, respectively. The analytical methodology thus developed was validated for total chromium using a Polish certified reference material Virginia Tobacco Leaves (CRM-CTA-VTL-2). The sum of the concentrations of Cr(VI) and Cr(III) was in good agreement with the total Cr in the CRM and with the total Cr determined after total digestion.