ELIMINATION OF COPPER INTERFERENCE BY CONTINUOUS-FLOW MATRIX-ISOLATION IN THE DETERMINATION OF SELENIUM BY FLOW-INJECTION HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY

A flow system incorporating a microcolumn of strongly acidic cation-exchange resin (Dowex 50W) to achieve continuous flow matrix isolation was used to eliminate copper interference in the determination of selenium by flow injection hydride generation atomic absorption spectrometry. The microcolumn manifold used for the selective retention of the copper interferent was interfaced with the hydride generation manifold through a flow injection sample injection valve. The two manifolds were made independent of each other in order to achieve optimum performance characteristics for both the matrix isolation and hydride generation. Following removal of the copper, a 400-mu-l sample was injected into a water carrier stream. This was merged with hydrochloric acid and subsequently with sodium tetrahydroborate soution. After introduction of argon, the selenium hydride was separated by a glass U-tube separator and atomized by a tube-in-flame atomizer. The intermittent regeneration of the column with 1 mol dm-3 HCl enabled repeated matrix isolation without any loss in resin efficiency or the need for column repacking and gives the option for total automation. The procedure was validated through accurate analyses of two copper metal reference materials, National Institute of Standards and Technology Standard Reference Material 454 Unalloyed Copper Xl and Bundesanstalt fur Materialforschung und -prufung, Germany, Certified Reference Material 361 Copper, containing 479 and 36-mu-g g-1 of Se(IV), respectively. The system was found to have a characteristic concentration of 1.0 ng ml-1, limit of detection of 2.1 ng ml-1, relative standard deviation of 1.5% (10 ng ml-1 Se(IV), n = 12) and sample throughput of 51 h-1.