Technical Notes

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This presentation focuses on the use of graphical tools to provide an intuitive understanding of how quadrupoles work. The graphical representations help to illuminate the correlation between the Mathieu stability diagram and peak width and mass calibration.  By mastering these basic graphical concepts, a firm foundation will be formed for a more rigorous treatment of quadrupole theory.   

This presentation approach is unique to any yet found in the literature, with its focus on practical implications of quadrupole theory, de-emphasizing the complex abstract equations typically utilized in traditional summaries of quadrupole theory.

The purpose of this presentation is to help demystify the theory associated with how quadrupoles operate, specifically with regards to the effects of variation of ion energy on peak shape. Using this graphical approach, quadrupole operation can be understood intuitively without extensive study of the equations of motion.
This presentation discusses what happens to transmission and resolution when you restrict the aperture at the exit of a quadrupole, and its affect on the shape of an ion beam as it exits a quadrupole. 
This presentation explores, through simulation and experiment, the changes in performance when the emissivity of the ion source is limited to be much smaller than the inscribed diameter of the quadrupole.
An examination of the theoretical basis and practical inplications of the use of pre-filters coupled to analytical quadrupoles to improve transmission and abundance sensitivity.  Calculated ion trajectories are used to illustrate ion motion, and calculated phase space acceptance ellipses are used to interpret experimental results. The goal of this work is to help build an intuitive understanding of how quadrupoles work, and more importantly, how to optimize the design of experiments involving quadrupoles.

There are a number of parameters which control quadrupole mass range and transmission, including rod diameter, RF frequency and rod length. With the trend toward miniaturization of analyzers, it is becoming increasingly important to minimize power and size requirements. The question is how small is too small? Mass resolution is very much dependent upon RF frequency, rod length and the energy of the ions as they transmit through the quadrupole. Mass range and voltage requirements are inversely proportional to both the square of rod diameter and the square of RF frequency. The fundamental question is whether an increase in RF frequency can offset the performance loss associated with a reduction in rod diameter. In this work, it was determined that for cases where the emissivive area of the ion source is much larger than the acceptance of the quadrupole, absolute transmission is approximately proportional to the square of RF frequency, and the cube of rod diameter.
This work compares and contrasts the transmission characteristics of hexapoles, round rod quadrupoles, and rectilinear quadrupoles.
This work explores the performance penalties associated with mass range extension of quadrupole devices through reduction in RF frequency. Mass range is proportional to frequency squared.  Halving the frequency quadruples the mass range, but at what expense in resolution and transmission?

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