INVESTIGATIONS OF THE RF-ONLY QUADRUPOLE MASS ANALYZER.

摘要

The performance of a quadrupole mass filter operated in the RF-only mode has been investigated. A discussion of both the formal and qualitative theories of quadrupole mass analyzers is given. Data is presented which demonstrates that the transmission properties of such devices deviate markedly from those which would be predicted from the Mathieu stability diagram. The transmission efficiency of ionic species, through an RF-only quadrupole, is shown to depend primarily on three factors. The first of these is the formal stability of the ion trajectory as summarized by the coordinates of the particle in a, q space. The second factor is the acceptance aperture of the quadruople in combination with the emittance of the ion source. The final factor is shown to be spacial focusing conditions which arise due to the nature of the frequency components that are contained within the trajectory of an ion as it traverses the quadrupole electrode structure. The theory of such spacial focusing conditions is reported. The measurement of naturally occurring isotope abundance ratios is used to demonstrate the magnitude of errors which may result due to the nonideal transmission properties of the RF-only quadrupole. Suggestions are provided to minimize such mass discrimination effects. Additional experiments dealing with the quadrupole notch filter are described. Performance of a unique voltage tuned quadrupole notch filter is demonstrated. The theory, design, and construction details of such a device are reported.