Noise power spectral characteristics of an inductively coupled plasma-mass spectrometer

Abstract

The noise power spectra of {sup 85}Rb{sup +} signal and {sup 93}Nb{sup +} signal from an inductively coupled plasma mass spectrometer were measured at the same plasma conditions as were those of Sr II emission from the plasma itself. Comparison of these spectra showed that discrete frequency noise in the emission at the mass spectrometer sampling orifice is nearly identical with that in the mass spectrometric signal and that white noise in the mass spectrometer signal was higher than that found in the emission signal. The dependence of noise frequencies on plasma operating conditions was generally the same for both measurements and was generally the same as that expected of emission from the plasma alone, i.e., when the plasma was not being sampled for mass spectrometry. However, discrete frequency noise in emission from the plasma alone differed substantially in frequency from that in the mass spectrometric signal. These results indicate that the plasma is the source of discrete frequency noise in the mass spectrometric signal and that the discrete noise frequencies can be affected by changes in plasma gas dynamics due to interaction between the plasma and the mass spectrometer sampling interface. The major source of signal instability in thismore » particular inductively coupled plasma mass spectrometer was found to be 1/f noise.« less