A sequential injection on-line column preconcentration system for determination of cadmium by electrothermal atomic absorption spectrometry

A sequential injection system for on-line sorbent extraction preconcentration in electrothermal atomic absorption spectrometry was developed for the determination of trace cadmium in seawater and other water samples. The system is characterized by simple manifold design and improved robustness. The Cd-APDC complex was sorbed on a 15-μl micro-column (located at the tip of the furnace sampling probe) packed with C 18 . After sequentially metering segments of ethanol, washing acid, sample and APDC complexing reagent into a 2.5-m-long, 1-mm-i.d. holding coil, the flow was reversed and directed to the column. The complexing reaction, sample loading and column washing were then achieved within the single reversed syringe stroke. The sorbed analyte was then eluted into the furnace with 50 μl ethanol. Mutual mixing between sample, washing acid, and eluent were prevented by separating the zones with small air segments during metering. Progressive tightening of the column was avoided by a short back-suction through the column after each operational cycle. With 1 ml sample loaded, and 50 μl eluate introduced into the furnace, an enrichment factor of 19 was obtained with a detection limit of 0.5 ng l −1 Cd (3σ), a precision of 2.1% R.S.D. ( n =11), and a throughput of 12 h −1 . Good recoveries were obtained for spiked water samples and good agreement of results with standard reference seawater and river water samples were achieved.