Vesicle-assisted determination of ultratrace amounts of cadmium in urine by electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry

Abstract

Two methods for the determination of ultratrace amounts of Cd, based on vesicular hydride generation, includingin situ trapping electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICP-MS), are described and compared for Cd determination in urine. The human urine samples are diluted 1+1 with ultrapure water and no other sample pre-treatment is necessary. Thus, the risk of contamination at basal or ‘normal’ metal levels in urine is minimized. Using flow injection hydride generation ICP-MS (FI-HG-ICP-MS), the detection limits observed for Cd in water and urine (50 µl sample volume) were 3.5 and 7 pg, respectively, and the observed relative standard deviation for ten replicate analyses of 50 µl of a 5 µg l–1 aqueous CD solution was ±3.2%. In situtrapping allows preconcentration in the graphite tube; by preconcentrating 1.4 ml of urine the detection limit achieved by ETAAS was 10 ng l–1 (14 pg, absolute). The use of silicone as an antifoam agent for vesicular cadmium hydride generation allowed a throughput of about 20 samples h–1 by FI-HG-ICP-MS detection. The concentration of Cd in human urine was evaluated directly by aqueous standard calibration as no matrix interferences were observed for both methods under study. NIST SRM 2670 Toxic Metals in Freeze-Dried Urine was analysed by the two methods with excellent results. The accuracy of the results was demonstrated in two ways because the reported values for the SRM agreed well with the results obtained using either of the two methods under investigation.