IMPACT OF BIAS VOLTAGE ON FURNACE ATOMIZATION PLASMA EMISSION-SPECTROMETRY PERFORMANCE

The effects of an applied d.c. bias potential on the analytical response from a furnace atomization plasma emission spectrometry (FAPES) source operating with a 50 W He plasma were investigated. Enhancements in absolute sensitivity and detection limits for B, Cd, Pb, Ni, Fe, S, Pt and Se ranged from 2-10-fold as compared to the usual ''free running'' self-bias situation and response from all species was enhanced as the applied bias was made more negative. Reflected power increases up to 35 W exert little effect on the excitation conditions within the plasma. The excitation temperature of the He support gas as well as that of Fe introduced as a thermometric species indicated that, while the temperature of the former varied by up to 700 K over the course of an atomization transient, that of Fe remained relatively stable. Bias control reduced the fluctuation in the He temperature to under 400 K.