Ultrasonic extraction of hexavalent chromium in solid samples followed by automated analysis using a combination of supported liquid membrane extraction and UV detection in a flow system

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 degrees 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 mu g l(-1) using a 5 mM phosphate buffer at pH 7.0 and 1.18 mu g 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 mu g l(-1) and 0.03 mu g 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.