CHARACTERIZATION OF A 9-MM TORCH FOR INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

A 9-mm torch and a 40.68-MHz radiofrequency power supply were evaluated for use in inductively coupled plasma mass spectrometry (ICP-MS). With this system, an analytically useful plasma can be supported at 850 W applied r.f. power and 8.7 l min-1 total argon flow-rate. The effects of operating parameters (nebuliser gas flow-rate, r.f. power, sampling depth and ion-lens voltages) on the analyte ion signals were determined. The 9-mm source exhibits greater independence of the ion-optic bias potential on relative atomic mass than do conventional-sized torches. Further, the 9-mm system produced similar sensitivities, detection limits, doubly charged ion ratios and oxide ion ratios to the conventional plasma but with lower power and argon consumption. However, the proper placement of the discharge under the interface was found to be critical to obtain maximum signal levels.