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A simple and sensitive supported liquid membrane (SLM) extraction technique for the determination of Cr(VI) in occupational hygiene and environmental samples has been developed. Solid samples were ultrasonicated for 30 min at 40 °C in ammonium or phosphate buffers. The samples containing Cr(VI) were extracted using the SLM technique for 20 min and Cr(VI) was determined on-line in a flow system by reaction with 1,5-diphenylcarbazide (DPC). The detection limits after a 20 min SLM enrichment at a flow rate of 1 ml min–1 were 0.63 µg l–1 using a 5 mM phosphate buffer at pH 7.0 and 1.18 µg l–1 using a 10 mM ammonium buffer at pH 8.0. The corresponding detection limits for an alternative approach using electrothermal atomic absorption spectrometry (GFAAS) off-line after 20 min SLM enrichment were 0.04 µg l–1 and 0.03 µg l–1 for ammonium and phosphate buffers, respectively. The method was validated using a new certified reference material for Cr(VI) and total leachable Cr in welding dust, CRM 545, from the European Commission’s Community Bureau of Reference (BCR). The method should be adaptable for both field sampling and analysis.

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 µg l–1. The relative standard deviation for lead concentrations in the range 4–20 µg 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 µg l–1 (standard deviation 1.8 µg l–1) which is within the recommended range of 9.2–10.8 µg l–1.