On-line ion exchange preconcentration in a sequential injection lab-on-valve microsystem incorporating a renewable column with ETAAS for the trace-level determination of bismuth in urine and river sediment

A sequential injection system for on-line ion-exchange separation and preconcentration of trace-level amounts of metal ions with ensuing detection by electrothermal atomic absorption spectrometry (ETAAS) is described. Based on the use of a renewable microcolumn incorporated within an integrated lab-on-valve microsystem, the column is initially loaded with a defined volume of beads of an SP Sephadex C-25 cation exchange resin. After having been exposed to a metered amount of sample solution, the loaded bead suspension is precisely manipulated within the valve to allow reproducible elution of the retained measurand by 30 mul of nitric acid (1:16,v/v), which then via air segmentation are transported into the graphite tube for quantification. The content of the used column is afterwards discarded and new column material is aspirated for the next run. The ETAAS determination is performed in parallel with the preconcentration process of the ensuing sample. The performance of the system is demonstrated for the determination of bismuth. With 2.4 ml sample loading, an enrichment factor of 33.4, a detection limit of 27 ng /l, along with a sampling frequency of 10 was obtained. The relative standard deviation was 2.3% for the determination of 2.0 mug/l Bi (n = 7). The procedure was validated by determination of bismuth in a certified reference material CRM 320 (river sediment), and by bismuth spike recoveries in two human urine samples.