Sequential injection on-line matrix removal and trace metal preconcentration using a PTFE beads packed column as demonstrated for the determination of cadmium by electrothermal atomic absorption spectrometry

A sequential injection (SI) on-line matrix removal and trace metal preconcentration procedure by using a novel microcolumn packed with PTFE beads is described, and demonstrated for trace cadmium analysis with detection by electrothermal atomic absorption spectrometry (ETAAS). The analyte is initially complexed with diethyldithiophosphate (DDPA) and adsorbed onto the column, which is afterwards eluted with 50 mul of ethanol and subsequently introduced via air segmentation into the graphite tube for quantification. The ETAAS determination is synchronized with sample pre-treatment in the SI system. No flow resistance is encountered at a flow rate of 9.0 ml/min through the column. The preconcentration efficiency was improved significantly by using the packed column as compared with a knotted reactor. With a 40 s sample loading time at 4.5 ml/l along with a sampling frequency of 16 s/h, quantitative adsorption of cadmium (99% retention efficiency) and an enrichment factor of 59.4 were obtained, as compared with only 46.7% and 28.0 by using a knotted reactor of similar internal surface area as the packed column. The detection limits and precision (RSD, 0.1 mug/l Cd) are at the same levels, i.e., 1.3 ng/l (LOD), 1.3% (RSD) for the packed column, and 1.2 ng/l (LOD), 1.5% (RSD) for the knotted reactor. The practical applicability of the procedure is demonstrated by the determination of trace levels of cadmium in three certified reference materials.