Effect of Rod Asymmetry on Field Distortions and Transmission Characteristics in Linear Quadrupole Mass Filters

TL;DR

This study investigates how small structural asymmetries in linear quadrupole mass filters introduce higher-order multipole components, affecting their transmission and resolution characteristics, using simulation analysis.

Contribution

It reveals the emergence and impact of octupole and hexadecapole components due to asymmetry, providing insights into their correlation with transmission performance.

Findings

Higher multipole components increase with asymmetry.

Transmission resolution correlates with multipole field strength.

Asymmetry affects the mass filter's performance and resolution.

Abstract

This article reports the appearance of the octupole and hexadecapole components in the radial potential, which are otherwise absent in a linear quadrupole mass filter of symmetric round-rod configuration, if a small structural asymmetry is introduced in one electrode. Using the commercial ion simulation package SIMION, it is shown that the weightage of the octupole and hexadecapole potential increases with an increase in the asymmetry factor. A consistent correlation is observed between the octupole and dodecapole components, and between the hexadecapole and icosapole components with asymmetry added to different rod-to-field radius ratios. The transmission characteristics of the mass filter are studied for different asymmetry factors and rod-to-field radius ratios. The variation in the resolution parameter, as derived from the transmission contour, exhibits a strong correlation with the combined weightage of the multipole fields.