EFFECT OF PRE-EVAPORATING THE SOLVENT ON THE ANALYTICAL PERFORMANCE OF INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The effect of heating the sample aerosol was studied by installing a h eated extension (at 400-degrees-C) between the spray chamber and the t orch. Both 5- and 2-mm i.d. extensions were characterized in terms of sensitivities and detection limits for aqueous solutions containing Al , V, Cr, Mn, Co, Ni, Zn, Ga, As, Mo, Cd, Sb, La and Pb. The best analy tical figures of merit were obtained with the 2-mm i.d. extension, whi ch resulted in detection limits being lowered to an average of 30% of those obtained with the traditional (i.e. extension-free) sample intro duction system. This improvement was greater than that expected from t he concurrent increase (by an average factor of 1.63) in sensitivities (including no change for Zn and Ga, and a degradation for Cd and Pb). The heated extension therefore significantly reduced noise as a resul t of the pre-evaporation process which decreased the average droplet s ize entering the plasma. The greatest improvement in sensitivity was o bserved for V, Mo and La, three elements forming relatively strong oxi des; investigations using Ce and Th (which form even stronger oxides) clearly showed that elements prone to oxide formation were experiencin g a shift in their optimum nebulizer flow rate toward that used for mu ltielemental analysis. Thus, the heated extension results in multielem ental conditions that are optimal for a wider range of elements.