Factorial designs for Cd, Cr, Hg, Pb and Se ultrasound-assisted acid leaching from human hair followed by atomic absorption spectrometric determination

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Abstract
An acid leaching procedure, for use as a sample pre-treatment, was developed for Cd, Cr, Hg, Pb and Se determination in human hair. A Plackett–Burman experimental design was used as a multivariate strategy for the evaluation of the effects of varying several variables at once. The effects on acid leaching of metals of nitric acid, hydrochloric acid and hydrogen peroxide concentrations, acid solution volume, exposure time to ultrasound, temperature of the ultrasonic bath, and hair particle size, have been investigated. From these studies, certain variables showed up as significant, and they were optimised by a 23 + star central composite design, which involved 16 experiments. Optimum values of the variables were selected for the development of acid leaching procedures to extract trace metals from human hair. Electrothermal atomic absorption spectrometry (ETAAS) was used to determine Cd, Cr, Pb and Se, while cold vapour-atomic absorption spectrometry (CVAAS) was used for Hg measurements. An acid digestion induced by microwave energy was used to obtain the total metal concentration and also for comparative purposes. IAEA-085 and NIES No. 13 certified reference materials, which offer certified values for some elements, were used in order to verify the accuracy of the methods.

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