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 microcolumn 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 microcolumn 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 part of the eluate (ca. 30 mul) is collected and introduced into the plasma via the DIHEN. The eluted beads are then discarded and a new column 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 (3s) are 15 ng l-1 (Ni) and 4 ng l-1 (Bi), while the sampling frequency is 12 h-1.

The precisions are 2.9% (0.8 mug l-1 Ni) and 1.7% (0.8 mug l-1 Bi), respectively. 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.