Anodic stripping voltammetric determination of total lead in anencephalic fetuses after pressure/temperature-controlled microwave mineralization

Abstract

The development of a closed-vessel mineralization method for the decomposition of brain, liver, kidney and lung specimens of anencephalic (A) fetuses and controls (C) from the eastern coast of lake Maracaibo, Venezuela, is presented. Digestion was done in a laboratory microwave oven provided with pressure sensing tube and fiberoptic temperature probe to monitor and control pressure and temperature conditions inside the lined digestion vessels. Total lead was subsequently determined by differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode. The optimized conditions for maximal pressure and temperature set up were 1260 kPa and 190 °C. Three samples and one blank were routinely prepared for simultaneous digestion. After sample mineralization, the lead oxidation peak appeared at a potential of −0.45 V vs. Ag AgCl , pH 4.70. Lead concentrations obtained by DPASV analysis of the mineralized biological materials were compared with those provided by electrothermal atomization atomic absorption spectrometry (ETA-AAS) on the same digestion samples. The correlation between the two methods was excellent: y = 1.142 x − 0.0035, r = 0.9999, n = 40, p < 0.001, where y and x were the lead concentrations determined by DPASV and ETA-AAS, respectively. For the DPASV determination of total lead, precision (R.S.D.) was better than 3.8%, for within- and between-run analyses. The detection limit of the electrochemical method, defined as three times the standard deviation of a blank solution, was 0.03 μg Pb g −1 (in solid sample), equivalent to 0.1 μg Pb l −1 in the diluted test portions. The dry-weight metal concentrations (± 1 S.D., μg g −1) found in brain, liver, kidney and lung were as follows: (brain, undetectable in A and in C; liver, 2.1 ± 1.1 in A, 0.5 ± 0.2 in C; right lung, 1.1 ± 0.8 in A, 0.6 ± 0.1 in C; left lung, 0.6 ± 0.2 in A, 0.7 ± 0.1 in C; right kidney, 1.4 ± 0.7 in A, 1.5 ± 0.03 in C and left kidney, 1.7 ± 0.9 in A, 0.7 ± 0.2 in C. The proposed DPASV method constitutes an analytical alternative, as reliable as ETA-AAS, for the voltammetric determination of total lead in solid samples.