On-line preconcentration cold vapour atomic absorption spectrometry for the determination of trace mercury in edible seaweeds

Possibilities for the use of an inexpensive sulfydryl cotton fiber (SCF) adsorbent to separate and preconcentrate traces of mercury from acid digests from edible seaweed have been evaluated. Commercial empty cartridges were filled with around 0.75 g of laboratory-made adsorbent and they were incorporated in the 5-way valve of an automatic flow injection analysis system. Traces of mercury in acid digests were pumped through the cartridges for 45 s (flow rate of 8.8 ml min(-1)) and then eluted from cartridges with 0.5 M hydrochloric acid and 1.0 M sodium chloride solution for 45 s at a flow rate of 5.8 ml min(-1). At the same time that mercury is eluted from the cartridges, the eluate is mixed with a 0.05% (m/v) sodium tetrahydroborate solution and the mercury cold vapour is swept through the atomization cell with an argon flow of 50 ml min. The overall procedure (mercury separation/preconcentration and mercury cold vapour generation/ atomization) is completed after around 90 s. The developed method implies an enrichment factor of 10.2 with a limit of detection of 5.23 ng g(-1). Repeatability of the overall procedure and accuracy were successfully assessed.