Flow injection on-line two-stage solvent extraction preconcentration coupled with ET-AAS for determination of bismuth tn biological and environmental samples

A robust flow injection/sequential injection(FIA/SIA) on-line two-stage solvent extraction separation/preconcentration procedure coupled to electrothermal atomic absorption spectiometry (ETAAS) is described and demonstrated for the determination of trace-levels of bismuth. In 1-4% (v/v) nitric acid medium, diethyldithiophosphate (DDPA) chelates bismuth and the chelating complex formed is extracted into isobutyl methyl ketone (IBMK), which is separated from the aqueous phase by means of cavity gravitational phase separation. Both single and two-stage separations are used. In each case, 40 mu l of the concentrate is entrapped and metered in a loop, and subsequently delivered via air-segmentation into a pyrolytically coated graphite tube. The ETAAS determination is performed in parallel with the preconcentration process of the ensuing sample. Enrichment factors of 17.8 and 31.5, detection limits of 12 ng l(-1) and 10.5 ng l(-1) for single and two-stage extractions, respectively, along with a sampling frequency of 13 h(-1) were obtained with 100 s of sample loading time at a sample flow rate of 5.4 mi min(-1). The relative standard deviations were 2.8% and 1.9% for single and two-stage extractions, respectively. The procedure was validated by determining the bismuth content in a certified reference material and in human urine samples.