Abstract

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 µl 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 µl) 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 µg l⁻¹) for Ni, and 9.1 (0.04–1.6 µg l⁻¹) and 28.4 (1.6–3.2 µg l⁻¹) for Bi. The detection limits (3σ) 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 µg l⁻¹ Ni) and 1.7% (0.8 µg 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.