Mineralization of biological materials prior to determination of total mercury by cold vapour atomic absorption spectrometry

Abstract

Mineralization procedures performed in Parr digestion bombs heated by either convection or microwave irradiation were used for acid decomposition of human whole blood and urine, lyophilized tuna and pond sediment samples. These alternative procedures were tested for their suitability to permit subsequent determination of total mercury by cold vapour atomic absorption spectrometry (CVAAS). No significant differences (p>0.001) were observed; y= 1.001 x– 0.339, r= 0.983 and n= 32, where y and x are the mercury concentrations in samples decomposed by convection and microwave heating, respectively. The detection limit (2σ) was 53 ng l–1, which corresponds to 159 pg of Hg for 3 ml of solution undergoing analysis. For 80 mg of biological material, mineralized and diluted to produce 10 ml of solution, the detection limit was 6.6 ng g–1 of Hg in the original solid samples. Accuracy was verified by analysing National Institute of Standards and Technology (NIST) Reference Material RM 50 Albacore Tuna; Control Blood for Metals 1 (OSSD 20/21 from the Behring Institute); Heavy-metal Urine Control (Contox No. 0140 Level II from Kaulson Laboratories) and National Institute for Environmental Studies (NIES) No. 2 Pond Sediment reference material. An RSD of 3.7% was found for both the within- and between-run precisions. The convection-heating digestion required a considerable time, about 12 h (including two 4 h cooling intervals); nevertheless, the method can be recommended for processing a large number of samples. Microwave mineralization was much faster (≈70 s). The proposed mineralization procedures, combined with CVAAS, were used to establish the mercury levels (mean ± 1 SD) in whole blood (11.2 ± 7.8 µg l–1) and urine (9.2 ± 3.6 µg l–1) of 35 healthy adults of Maracaibo City who had not been occupationally exposed to mercury, and in whole blood (20.8 ± 7.9 µg l–1) and urine (19.7 ± 7.5 µg l–1) of 35 occupationally exposed subjects. The commercial tuna analysed showed a mercury concentration of 1.45 ± 0.09 µg g–1. The destruction of the organic matter was efficiently achieved by using both mineralization procedures, to a point where the analyte element was liberated from its chemical bonding and total mercury quantification was reliably accomplished by CVAAS.