ONLINE SPECIATION OF MERCURY AND METHYLMERCURY IN AQUEOUS SAMPLES BY CHROMATOGRAPHY ATOMIC FLUORESCENCE SPECTROMETRY AFTER HYDRIDE GENERATION

A method is described for the determination of picogram amounts of ino rganic mercury(II) and methylmercury(II) compounds in seawater. These compounds are first volatilized from the water samples by reduction to mercury (Hg-0) and formation of methylmercury hydride (CH3HgH) by mea ns of a sodium borohydride (NaBH4) solution and cryogenically focused onto a chromatographic stationary phase. Both mercury compounds are el uted according their boiling points and are passed through a pyrolysis tube, at 900 degrees C, before entering the atomic fluorescence detec tor. Absolute detection limits (3 sigma) are 1 and 2 pg for, respectiv ely, inorganic mercury and methylmercury. For seawater analysis, detec tion limits of 0.1-1.0 ng l(-1) can be achieved.