Detection of titanium in electrothermal atomizers by laser-induced fluorescence. Part 2. Investigation of various types of atomizers

Abstract

Different types of electrothermal atomizers (graphite and tungsten furnaces) have been studied for the determination of Ti by laser-induced fluorescence (LIF). It was found that all graphite furnaces suffer from both bulk contamination by Ti, corresponding to tens of pg per firing, and significant memory effects in such a way that the high sensitivity of the LIF technique could not be fully utilized. The detectability of Ti by the LIF technique was limited by fluctuations of the atomizer blank signals and therefore depended mainly on the Ti history of the furnaces. The detection limit of Ti was found to be similar for all graphite furnaces: around 1 pg for furnaces not exposed to any substantial amounts of Ti, and a few pg for those which had been exposed to a few hundreds of pg of Ti (or more). It was found that the transversely heated graphite atomizer (THGA) from Perkin-Elmer gives the most reproducible atomization of Ti. The tungsten furnace showed no memory effects and therefore no empty firings (burn-outs) between determinations are needed. The tungsten furnace, however, afforded significantly weaker signals (approximately 250-fold) than the graphite furnaces; this was attributed to incomplete atomization processes. The Ti signal from the tungsten furnace could be increased by the addition of H 2 in the buffer gas. For 20% of H 2 added, however, the analyte signal was still weaker by a factor of 8 than that seen in a graphite furnace shielded with Ar (the remaining difference is primarily attributed to fluorescence quenching from H 2). In addition, the precision of the measurements was poorer than that obtained from graphite furnaces.