The role of discrete sample injection in trace mercury analysis by atomic fluorescence spectrometry

Coupling specific atomic fluorescence spectrometers to vapour generation techniques is a highly sensitive approach to the determination of trace levels of mercury. In many sample types the levels of the mercury content are extremely high and the matrix may have a deleterious e2ffect on the measurement. This paper discusses the application of discrete sample injection techniques to broaden the range of analytes tested and the levels analysed. The limitation of linear dynamic range for fluorescence is the self-absorption e/ffect. Reducing the eective sample size to below 100 # litres allows a linear calibration up to 10 parts per million (ppm). This sample limitation, coupled to the software's ability to reset the sampling valve should the signal level exceed the maximum setting, ensures that levels of up to lOOppm can be presented to the analyser. An additional advantage of the discrete sample injection applies to complex analytical samples, for example concentrated sulphuric acid. The eective dilution provided by this means overcomes any matrix interferences and quickly provides correct data. With proper care, the analytical range of the system described can extend over seven orders of magnitude from less than 1 part per trillion (ppt) through to 10 ppm.