Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion.

Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO(3) into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l(-1); the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6-3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100-106% range. Zinc and cadmium were determined by FAAS. The limit of detection for zinc determination was 0.078 mg l(-1); the R.S.D. for zinc contents was in the 0.8-8.6% range. A limit of detection of 0.09 mg l(-1) was obtained for cadmium determination; the R.S.D. for cadmium contents was in the 0.7-2.7% range. The determinations were performed after two different sample mineralization pre-treatments - dry ashing (in an electric furnace) and wet mineralization (in a microwave oven). Both methodologies provided comparable results for zinc and cadmium determination in shampoos. The proposed microwave assisted digestion procedures allow a precise and accurate determination of selenium, zinc and cadmium in commercial antidandruff shampoos, and the sample pre-treatment is less time-consuming than the classic methods.