On-line pre-concentration of Hg in blood and urine and determination by CVAAS

Abstract

A method for total Hg determination in urine and blood by cold vapour atomic absorption spectrometry (CVAAS), after on-line separation/pre-concentration, is described. The samples were acid-digested in closed vessels using a HNO₃/HClO₄ mixture and heating in a microwave oven. The Hg determination was accomplished by retention of Hg complexes formed with the ammonium salt of O,O-diethyldithiophosphoric acid (DDTP) on C₁₈ immobilized on silica in a column. The analyte was eluted with methanol, which was mixed with a reducing agent (NaBH₄) on-line, and measured. The optimum conditions for the Hg pre-concentration, such as DDTP concentration, acid concentration and acid nature (HNO₃ and HCl), and the solutions flow rates were experimentally established. The conditions for on-line cold vapour generation, including the acid concentration in the eluant (methanol), the NaBH₄ concentration and the carrier gas (Ar) flow rate, were optimised. The limit of detection (LOD), based on three times the standard deviation of the sample blank (10 consecutive measurements), of the proposed method was 8 ng l⁻¹ of Hg (by processing 7.6 ml of solution) and the LOD for Hg in the samples was 20 ng l⁻¹. At a concentration of 50 ng l⁻¹ of Hg solution, the relative standard deviation was less than 6% for five replicates of the sample solution or calibration solution. The calibration curves were linear from 25 ng l⁻¹ to 600 ng l⁻¹ of Hg and a sample throughput of 24 measurements per hour was possible. The accuracy of the method was checked by analysis of a certified urine sample and spiked blood samples. The proposed method was employed for analysis of real blood and urine samples.