Determination of total chromium and chromium(VI) in animal feeds by electrothermal atomic absorption spectrometry

Abstract

An electrothermal atomic absorption spectrometric method was developed for the determination of total and hexavalent chromium in animal feeds. For measuring total chromium the samples were digested in a mixture of three acids (HNO₃–HCl–HF). Chromium in its hexavalent state was dissolved in 0.01 mol l^–1 NaOH solution. A mixture of Pd + Mg was used as a chemical modifier. Extensive validation of the proposed method was carried out both by the standard additions method and by analysis of National Institute of Standards and Technology Standard Reference Material 1548 Total Diet. The detection limits were 0.53 and 0.42 µg l^–1 for total and hexavalent chromium, respectively. Measurements can be made over a linear range between 0.53 and 50 and 0.42 and 50 µg l^–1 for total and hexavalent chromium, respectively. The relative standard deviations were 4.5 and 7.0% for total and hexavalent chromium, respectively, hence the proposed method is satisfactory for routine analyses. In 70 samples that were analysed the mean levels found were 1.93 µg g^–1(0.20–6.87 µg g^–1) and 230 ng g^–1(10.0–780 ng g^–1), for total chromium and chromium(VI), respectively. The large variations in the levels of metal found in the analysed feeds shows diverse contamination of the raw materials used in the preparation of the samples.