Determination of mercury by continuous flow cold vapor atomic fluorescence spectrometry using micromolar concentration of sodium terahydroborate as reductant

Systematic experiments were conducted to evaluate and compare the analytical figures of merit of two reducing agents (SnCl2 and NaBH4) in a continuous flow cold vapor atomic fluorescence mercury analyzer. It was found that sodium tetrahydroborate can efficiently reduce Hg2+ in various environmental samples at a concentration as low as 10 muM (ca. 3.8 x 10(-5) % w/v). Most commonly encountered transition metals (Fe2+, Fe3+, Zn2+, Cu2+, Ni2+, Pb2+ and Cr3+) did not interfere with total Hg determination. No interference from hydride-forming elements (Se4+, Sb3+ and As3+) was observed. Interference caused by Mn2+ and Ag+ could be readily removed by dilution and by using appropriate modification of the reaction matrix. A higher concentration of NaBH4 (0.1 M) is stable for 1 month when stored in the NaOH matrix (0.2 M) and at low temperature (4degreesC). A working solution of NaBH4 can be freshly prepared by dilution. With NaBH4, the whole continuous flow system is kept clean much more easily as no precipitate is formed, which in turn considerably reduces memory effects, simplifies analytical operation and reduces the chemical cost six-fold.