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

An acid leaching procedure, for use as a sample pre-treatment, was develope d 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 le aching of metals of nitric acid, hydrochloric acid and hydrogen peroxide co ncentrations, acid solution volume, exposure time to ultrasound, temperatur e of the ultrasonic bath, and hair particle size, have been investigated. F rom these studies, certain variables showed up as significant, and they wer e optimised by a 2(3) + star central composite design, which involved 16 ex periments. Optimum values of the variables were selected for the developmen t of acid leaching procedures to extract trace metals from human hair. Elec trothermal atomic absorption spectrometry (ETAAS) was used to determine Cd, Cr, Pb and Se, while cold vapour-atomic absorption spectrometry (CVAAS) wa s used for Hg measurements. An acid digestion induced by microwave energy w as used to obtain the total metal concentration and also for comparative pu rposes. IAEA-085 and NIES No. 13 certified reference materials, which offer certified values for some elements, were used in order to verify the accur acy of the methods.