Approaches to the improvement of quantitative precision in selected ion monitoring: High resolution applications

Abstract

A MAT 731 mass spectrometer has been modified to permit multiple ion monitoring at resolutions of 8000–10 000. The greater imprecision in response ratio (analyte/internal standard) determinations which accompanies the increase in mass spectrometric resolution is attributable to the weaker signal detected, rather than to instrument instability. The mass spectrometer has been coupled to a microprocessor-based data system and software prepared to facilitate the precise determination of response ratios. Imprecision is markedly reduced when isotope ratios are determined by linear regression analyses of signals attributable to the two ionic species detected.