Multi-channel background correction technique for pulsed laser-excited atomic fluorescence spectrometry with a graphite furnace

Abstract

A multi-channel background correction technique for pulsed laser-excited atomic fluorescence spectrometry with electrothermal atomisation (ETA-LEAFS) is described. The background signal is measured simultaneously with the analyte signal using three optical fibres positioned at the exit slit of the monochromator and coupled to two different photomultiplier tubes. In this way the measurement of the background signal can be restricted to exactly the same period of time as that of the analyte signal, which is necessary for obtaining the highest possible correlation between the analyte and background signals. The applicability of ETA-LEAFS with this background correction technique was demonstrated for gallium at 2800 K. A detection limit of 0.05 pg of gallium in aqueous solution was obtained for the corrected signal. It was shown that black-body radiation, scattered laser light and molecular fluorescence can be corrected for by the simultaneous background correction technique. The concept of limiting sources of noise in ETA-LEAFS is discussed. It is argued that the limiting source of noise is often the shot noise rather than the instrumentation noise.