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Capillary electrophoretic determination of trace metals in hair samples and its comparison with high performance
S McClean1, E O'Kane, D J Coulter
1ABCS School, University of Ulster, Coleraine, Northern Ireland.
Abstract:
Capillary electrophoresis (CE) is compared with high performance liquid chromatography (HPLC) and atomic absorption spectrometry (AA) for the determination of trace concentrations of selected metals in human hair. CE and HPLC methods are based upon the chelation of the metals with 2-(5'-bromo-2'-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) followed by ultraviolet-visible (UV-Vis) detection. Large volume sample stacking (LVSS)-CE using injection times of up to 300 s is applied to the simultaneous determination of Co and Zn providing lower limits of detection (LODs) of 4.2 x 10(-8) mol dm(-3) and 6.0 x 10(-8) mol dm(-3), respectively, than can be achieved by conventional CE. The LVSS procedure could not be applied to hair samples due to a higher run current existing when the sample is introduced into the capillary. Conventional CE with cetyltrimethylammonium bromide (CTAB) present in the run buffer to retain the ligand in solution is used for the determination of metal concentrations in hair samples. Only Zn could be determined in this way as it exists at relatively high levels in hair. Co, Ni and Hg could be detected when spiked hair samples were analysed with estimated LODs of 5.0 x 10(-7) mol dm(-3), 1.0 x 10(-6) mol dm(-3) and 3.0 x 10(-5) mol dm(-3), respectively. HPLC was successfully used to determine Co and Cu in hair samples, with levels of 57.6 ppb and 17.31 ppm being found, respectively, and corresponded closely to results produced by AA. Fe also gave a signal together with unidentified coeluting species. In a separate HPLC study the determination of Ni and Hg as their complexes with hydrogen peroxide and 5-Br-PADAP was also investigated and LODs of 2.0 x 10(-6) mol dm(-3) and 5.0 x 10(-6) mol dm(-3), respectively, were achieved. AA was used as a reference method to determine levels of Co, Cu, Fe, Pb and Zn in hair and the results produced were in order of magnitude agreement with accepted literature values.