DETERMINATION OF TOTAL MERCURY IN SCALP HAIR OF HUMANS BY GOLD AMALGAMATION COLD VAPOR ATOMIC-ABSORPTION SPECTROMETRY

Cold vapour atomic absorption spectrometry (CVAAS) with a laboratory-b uilt system using a Au-Pt grid for mercury amalgamation, was applied i n the determination of total mercury (Hg-T) in human scalp hair. Two s ample dissolution procedures by HNO3 digestion were tested and compare d: in a poly(tetrafluoroethylene) (PTFE) bomb for 1.5 h at 110-degrees -C (procedure 1), and in sealed Pyrex ampoules for 24 h at 50 +/- 10-d egrees-C (procedure 2). After optimization of the aeration gas flow ra te (1 00 ml min-1), de-amalgamation temperature (700-degrees-C) and re leasing time (19 s), the analytical methodology was characterized and validated. The linear working range extended from 0.5 to 12.5 ng, and the characteristic mass was 0.29 ng of Hg (mass of analyte giving an a bsorbance of 0.0044). The repeatibility of measurements (within-day va riation), expressed as percent relative standard deviation (RSD%) was 5.5% at 1.25 ng of Hg (n = 8) and 3.7% at 12.5 ng (n = 14), and the me an reproducibility (between-day variation), estimated from calibration curves on different days, was 6.4 +/- 1.1% (n = 5). The absolute dete ction limit (3 x sigma(b) was 0.1 3 ng of Hg and the limit of quantita tion (1 0 x sigma(b)) was 0.43 ng of Hg (almost-equal-to 0.11 mg kg-1 in hair). Analytical precision (8.4 +/- 4.0% RSD) and accuracy (4.7 +/ - 2.5% mean relative error) were satisfactory for ppm and sub-ppm leve ls of Hg-T in several biological and environmental certified and stand ard reference materials (CRMs and SRMs) including hair. Procedure 2 wa s selected as it is much simpler, requires inexpensive reagents and is more amenable for routine application. Mean recovery of Hg-T in hair spiked with Hg standard solutions was 105% in the range 0.83-1.27 mg k g-1. In addition, two human head hair samples were assayed as prospect ive laboratory control materials. Thus, sub-sample homogeneity, analyt ical intra-laboratory variability and external quality control were as sessed to confirm the methodology in use. Between-day variation in hai r analysis for Hg-T conducted on pooled scalp hair over a period of 5 months was 4.8% RSD (1.10 +/- 0.053 mg kg-1 for the 95% confidence int erval; n = 16). Instrumental neutron activation analysis used as an in dependent method, showed significant correlation in results with CVAAS , both in several biological and environmental SRMs and CRMs and in hu man hair samples of pregnant and nursing women (Hg concentration range = 0.1 - 6.9 mg kg-1; n = 21; r2 = 0.880, p < 0.0001).