SUPPORTED LIQUID MEMBRANE COUPLED ONLINE TO POTENTIOMETRIC STRIPPING ANALYSIS AT A MERCURY-COATED RETICULATED VITREOUS CARBON ELECTRODE FORTRACE-METAL DETERMINATIONS IN URINE

A method for trace metal determinations in complex matrices is present ed, The method combines supported liquid membrane (SLM) sample clean-u p and enrichment with potentiometric stripping analysis (PSA) in a flo w system using reticulated vitreous carbon (RVC) as the electrode mate rial, The membrane contained 40% mim di-2-ethylhexylphosphoric acid di ssolved 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 ele ctrodeposition on the RVC electrode at -1.0 V (versus Ag/AgCl) was per formed simultaneously, The influence of various experimental parameter s such as deposition time, deposition potential and flow rate on the l ead signal was investigated, With a 10 min SLM enrichment including a 5 min deposition time, the detection limit for lead was 0.3 mu g l(-1) , The relative standard deviation for lead concentrations in the range 4-20 mu g 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 r unning a reference urine sample, The result obtained (five replicates) was 9.7 mu g l(-1) (standard deviation 1.8 mu g l(-1)) which is withi n the recommended range of 9.2-10.8 mu g l(-1).