Abstract
A method for the determination of total chromium in cocaine and heroin by flameless atomic absorption spectrometry is presented. Cocaine samples were dissolved in 2 ml of HNO 3 35.0% (v/v) and diluted to 10 ml with ultrapure water; heroin samples were dissolved in ultrapure water, adding 0.4 ml of HNO 3 35.0% (v/v) to dissolve inert species, and also diluted to 10 ml. Mg(NO 3) 2 and HNO 3, as chemical modifiers, were compared in terms of sensitivity, precision and accuracy, a lower detection limit being obtained for the use of Mg(NO 3) 2, 5.77 μg kg −1 (7.23 μkg −1 for HNO 3). Within-batch precision was found to be 6.19% and 1.48% for drug solution spiked with 0 and 10 μg l −1 of Cr 3+, respectively, when using Mg(NO 3) 2, and 7.45 and 1.19% for the same respective concentration levels when using HNO 3. Similar results on analytical recovery were obtained for both Mg(NO 3) 2 and HNO 3. Mg(NO 3) 2 was selected as the more adequate of the two chemical modifiers. A study of the introduction of a cooling-down step of 50 °C was carried out and compared in terms of sensitivity to the programme without a cooling-down step, but no advantage was observed. Studies on the variation in precision and analytical recovery with the amount of sample, and interferent effects of different species on chromium determination were developed. Finally, chromium concentrations obtained in cocaine samples varied between 0.02 and 0.14 mg kg −1, the levels in the heroin samples being in the 0.05–0.59 mg kg −1 range.
Published Version
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