Comparative study of 27.12 and 40.68 MHz inductively coupled argon plasmas for mass spectrometry on the basis of analytical characteristic distributions

Abstract

Analytical characteristics of 27.12 and 40.68 MHz inductively coupled argon plasmas (Ar-ICP) are compared as an ion source for mass spectrometry on the basis of distribution measurements. Analyte ion signals at 27.12 MHz are found to be more sensitive than at 40.68 MHz, which is based on the count ratio of analyte ion-to-plasma support Ar⁺. The r.f. power does not affect the ion counts at 27.12 MHz, but the signals are increased with r.f. at 40.68 MHz. The ratio of monoxide-to-singly charged ions is higher at 27.12 MHz for Y⁺ and Pb⁺, but the ratio of doubly-to-singly charged ions depends on the elements. The secondary discharge, more strongly observed at 40.68 MHz, might reduce monoxide ion formation. The proportion of the analyte ion (calculated from the ratio of analyte-to-total ion signal in the plasma) is highest in a 27.12 MHz ICP operated at 1.0 KW. Less interference and a wide range of ion kinetic energy distribution in the analytes are observed at 40.68 MHz. The average of the detection limits at 27.12 MHz is slightly lower than at 40.68 MHz.