A high voltage spark discharge was used to sample ferrous alloy samples in a point-to-plane configuration. An enclosed Petry spark stand was used so that the effluent from the spark could be put into a microwave discharge sustained at 2450 MHz. The emission from the eroded metals in the microwave discharge was monitored with a PARC Vidicon detector. This method of detection provided spectral simplification and improved signal-to-background ratios up to six-fold over the emission observed from the spark discharge. The emission from the microwave was shown to be linear with concentration for many lines observed.
Deborah J. C. Helmer and J. P. Walters, "Analysis of the Effluent from a High Voltage Spark Discharge with a Microwave-Induced Plasma," Appl. Spectrosc. 38, 392-398 (1984)