A method for trace metal determinations in complex matrices is presented. The method combines supported liquid membrane (SLM) sample clean-up and enrichment with potentiometric stripping analysis (PSA) in a flow system using reticulated vitreous carbon (RVC) as the electrode material. The membrane contained 40% m/m di-2-ethylhexylphosphoric acid dissolved in kerosene. Lead was used as a model substance in high-purity water and urine samples. The samples were enriched after a simple pH adjustment. The SLM enrichment time was 10 min when the last 5 min electrodeposition on the RVC electrode at -1.0 V (versus Ag/AgCl) was performed simultaneously. The influence of various experimental parameters such as deposition time, deposition potential and flow rate on the lead signal was investigated. With a 10 min SLM enrichment including a 5 min deposition time, the detection limit for lead was 0.3 microgram l-1. The relative standard deviation for lead concentrations in the range 4-20 micrograms l-1 was 0.05%. The overall SLM-PSA system was found to be stable for at least 100 urine analyses. The method was validated by running a reference urine sample. The result obtained (five replicates) was 9.7 micrograms l-1 (standard deviation 1.8 micrograms l-1) which is within the recommended range of 9.2-10.8 micrograms l-1.
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Djane et al. (1998) studied this question.
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