A portable device for continuous analysis of dissolved gaseous mercury in natural waters

A fully automatic device for continuous analysis of DGM (Dissolved Gaseous Mercury) concentration in natural waters, controlled by a Notebook, with a resolution time of 10-15 min, equipped with an Atomic Absorption Spectrometer with a detection limit of 0.5 pg, is described. A particular feature of this instrument is the portability, making its use suitable in remote locations by means of a car battery. Comparison of the results obtained using the device in the continuous mode and in the discrete mode shows good agreement taking into consideration that water samples were collected with shifting sampling times. To compare samples collected at the same time, a second analytical device, running in the discrete mode, was used. In this case results show that measurements performed with the discrete mode are slightly higher than the continuous one. Avoiding the sample handling it was possible to reduce the contamination from external sources and to achieve low instrumental blank values (1-2 pg). The field performance of this portable instrument was tested on seawater and lagoon water, where the DGM daily behaviour was measured. In agreement with several authors, a time shifting between DGM and solar radiation intensity higher than the instrumental resolution time was noted.