Coupling on-line preconcentration by ion-exchange with ETAAS. A novel flow injection approach based on the use of a renewable microcolumn as demonstrated for the determination of nickel in environmental and biological samples

A novel way of exploiting flow injection/sequential injection (FIA/SIA) on-line ion-exchange preconcentration with detection by electrothermal atomic absorption spectrometry (ETAAS) is described and demonstrated for the determination of trace-levels of nickel. Based on the use of a renewable microcolumn incorporated within an integrated micro FI-system, the column is loaded with a defined volume of small beads of an SP Sephadex C-25 cation-exchange resin and subsequently exposed to a metered amount of sample solution. However, instead of eluting the retained analyte from the organic ion-exchange resin, the beads are along with 30 mul of carrier (buffer) solution transported via air segmentation directly into the graphite tube, where they are ashed during the pyrolysis and atomization process. The ETAAS determination is performed in parallel with the preconcentration process of the ensuing sample. An enrichment factor of 72.1, a detection limit of 9 ng l(-1), along with a sampling frequency of 12 h(-1) were obtained with 150 s of sample loading time at a sample flow rate of 12 mul s(-1) (corresponding to 0.72 ml min(-1)). The relative standard deviations were 3.4%. The procedure was validated by determination of the nickel contents in two certified reference materials and in a human urine sample. (C) 2000 Elsevier Science B.V. All rights reserved.