Abstract: Amethod for determination of ultra-trace amounts of molybdenum in seawater by flow injection on-line sorbent extraction preconcentration coupled with GFAASis described.An approach for introducting only the most concentrated fraction of the eluate into the graphite tube while discarding the rest was investigated. The experimental parameters of the FI-GFAASwere optimized. If miniflow (50 mL/min) in atomisation step was used, the memory effect in the determination of molybdenum by graphite furnace could be removed. By using the preheating step in furnace temperature program, diffusion losses of molybdnum ethanol solution could be prevented. On-line chelation of molybdenum with dithiocarbamate (NaDDTC) and sorption of the complex on C¹⁸ sorbent packed in a micro column ensure high group selectivity and enrichment. The closed nature of flow system reduced the risk of contamination significantly. The enrichment factor was 13. 3 using sample loading volume of only 1. 35 mL, detection limit achieved was 0.027μg/L. Results obtained for seawater and riverwater standards agreed well with certified values with a good precision.

Key words: Flow-Injection, Sorbent extraction, GFAAS, Preconcentration, Molybdenum