Interfacing sequential injection on-line preconcentration using a renewable micro-column incorporated in a 'lab-on-valve' system with direct injection nebulization inductively coupled plasma mass spectrometry

A sequential injection (SI) on-line 'lab-on-valve' separation/preconcentration system incorporating a renewable ion-exchange micro-column interfaced with inductively coupled plasma mass spectrometry (ICP-MS) via a home-made direct injection high efficiency nebulizer (DIHEN) is described. Aimed at eliminating spectroscopic and non-spectroscopic interferences, the renewable micro-column is first loaded by aspirating 15 mul of a SP Sephadex C-25 cation-exchanger bead suspension and then exposed to a defined volume of sample solution. Residuals of matrix components are pre-eluted with carrier solution (nitric acid, 1 : 80 v/v), and the measurands are subsequently eluted with a defined volume of nitric acid (1 : 16 v/v). The leading volume of eluate (ca. 30 mul) is collected and introduced into the plasma via the DIHEN. The eluted beads are then discarded and a new column is aspirated for the next operation. Data acquisition is performed in parallel with the ensuing preconcentration process. With 2.0 ml sample loading, the enrichment factors are 35.2 (0.05-2.4 mug l(-1)) for Ni, and 9.1 (0.04-1.6 mug l(-1)) and 28.4 (1.6-3.2 mug l(-1)) for Bi. The detection limits (3 sigma) are 15 ng l(-1) (Ni) and 4 ng l(-1) (Bi), while the sampling frequency is 12 per hour. The precisions are 2.9% (0.8 mug l(-1) Ni) and 1.7% (0.8 mug l(-1) Bi). The procedure is validated by determination of nickel and bismuth in a certified reference material (CRM 320, River Sediment), and the recoveries are measured by spiking two human urine samples.