ANALYTICAL AND SPECTROSCOPIC CHARACTERIZATION OF DOUBLE-RESONANCE LASER-INDUCED FLUORESCENCE OF GOLD ATOMS IN A GRAPHITE-FURNACE AND IN A FLAME

Two excimer laser-pumped dye lasers were utilized to excite gold atoms in a graphite furnace to a high level whose energy is about 1.5 eV lo wer than the ionization potential of the atom, Collisional coupling po pulates several levels close to that reached by the second laser step, from which fluorescence is observed longitudinally with a pierced, pl ane mirror and detected with a solar blind photomultiplier. The lasers are tuned to 267.595 and 406.508 nm, respectively, while the fluoresc ence is measured around 200 nm. Several other excitation-detection sch emes are possible and are discussed. The best detection limit obtained , for a signal-to-noise ratio of 3, was 3 fg as absolute amount in the furnace, or 0.15 pg ml(-1). since a sampling volume of 20 mu l was us ed. A system in which the vapour produced in the furnace is swept into a small flame and the resulting fluorescence observed with the solar blind photomultiplier was also tested and found to be flame background noise limited, with a detection limit of 8 pg (0.4 ng ml(-1)). The te chnique was developed in order to determine trace levels of gold in si ze-segregated, atmospheric particulate samples.