On-line flow injection solid sample introduction digestion and analysis: spectrophotometric and atomic absorption determination of iron, copper and zinc in multi-vitamin tablets

An on-line flow injection system with solid sample introduction, digestion, treatment and analysis was proposed. The solid sample powder is inserted into a special chamber and carried by the digestion solution to a thermally heated PVC coil (1.4 mm i.d,). The analyte metal as the chloro-complex was retained on a coarse-particle (> 0.5 mm) anion exchange resin mini column. The resin beads are held between two plastic screens which allow insoluble residue to pass through to waste. After a brief column wash, the analyte is eluted with diluted HNO3 and determined spectrophotometrically or by atomic absorption. The proposed novel configuration of the multi-channel pinch valve allows handling slurries without tube blockage or valve damage. The system performance was tested by the determination of Fe, Zn and Cu in multi-vitamin tablets. Fe was determined spectrophotometrically as the thiocyanate complex while Zn and Cu were determined by atomic absorption. Compared with conventional digestion and analysis procedures the flow system yields a reasonably accurate relative error(RE) <2% and precise results with relative standard deviation (R.S.D.) in the range of 2.5-4.2%. (C) 2000 Elsevier Science B.V. All rights reserved.