Signal and noise considerations of non-dispersive laser-excited atomic fluorescence in a graphite tube atomiser with front-surface illumination

Abstract

A commercial graphite tube electrothermal atomiser (ETA) was used as an atom cell for laser-excited atomic fluorescence spectrometry (LEAFS). From the point of view of signal to noise ratio (S/N), both transverse and front-surface illumination of the furnace were investigated, together with dispersive and non-dispersive fluorescence detection. Front-surface illumination offered better sensitivity, due to better illumination efficiency, than transverse detection. Non-dispersive detection had better light gathering power, hence better sensitivity, than dispersive detection. The effects of optical filter bandpass and slit-width on the S/N of non-dispersive detection were explored. Narrow bandpass filters cut down the noise and led to improvements in limits of detection (LOD). Sub-femtogram (sub-10^–15 g) LODs for TI and Pb were obtained by using very narrow (1-nm) bandpass filters and non-dispersive detection of the fluorescence.