On-line preconcentration and in situ photochemical vapor generation in coiled reactor for speciation analysis of mercury and methylmercury by atomic fluorescence spectrometry

On-line preconcentration and in situ photochemical vapor generation in a coiled reactor was proposed for speciation analysis of ultratrace mercury and methylmercury (Hg2+ and MeHg+) by using atomic fluorescence spectrometric detection. Diethyldithiocarbamate (DDTC) served here not only as a chelating reagent to form hydrophobic compound of mercury for on-line preconcentration but also as a reductant for in situ photochemical vapor generation and desorption of mercury from the coiled reactor. Optimum conditions for on-line preconcentration and in situ photochemical vapor generation, as well as potential speciation analysis of Hg2+ and MeHg+, were carefully investigated. Limit of detection (LOD, 3 sigma) of 0.004 mu g L-1 or 0.0008 mu g L-1 for Hg2+ was obtained based on 40 s or 200 s of sample loading time, respectively, and it can be further improved by prolonging the sample loading time when necessary. The linear working range was in the range of 0.02-8 mu g L-1 with 40 s sample loading time. A precision of 4.5% RSD was achieved with mercury concentration of 2 mu g L-1. The proposed method can be applied for rapid speciation analysis of Hg2+ and MeHg+ by controlling the desorption and photochemical vapor generation conditions. The accuracy of the proposed method was evaluated by analysis of certified reference materials including water samples (GBW 080392 and GBW 080393), fish muscle (GBW 10029), and human hair (GBW 09101b), as well as National Research Council Canada DORM-2 fish muscle tissue. This is a simple, ultrasensitive and relatively green method for the determination of mercury and methylmercury.