EXTRACTION DISCHARGE SOURCE FOR INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY - SPECTRAL LINEWIDTHS AND INTERFERENCE EFFECTS

A supplementary electrical discharge is generated by extracting the axial channel of an Ar inductively coupled plasma (ICP) through a circular (0.5 mm diameter) sampling orifice into a small vacuum chamber. Emission is observed from just outside the sampling orifice and from the adjacent region of the plasma upstream of the sampler. The discharge enhances the intensities of several Ca II and Sc II lines but does not broaden the lines or otherwise perturb the line shapes. The sampling orifice does not introduce any additional memory or extend the rinse-out time required to change samples. Sodium concomitant at concentrations up to 1000 mg l-1 suppresses the intensities of analyte lines by 5-30%, depending upon the particular line involved. Sodium at 5000 mg l-1 suppresses either ion lines or neutral atom lines by 40-60%. This suppression effect is more severe than that generally observed under normal operating conditions when observing emission from the ICP alone. The additional suppression is attributed to a change in the spatial distribution of emission induced by the discharge and the gas flow into the sampler.