Mass selectivity of dipolar resonant excitation in a linear quadrupole ion trap. (23rd January 2014)

• Record Type: Journal Article
• Authors: Douglas, D. J.; Konenkov, N. V.
• Is Part Of: Rapid communications in mass spectrometry. Volume 28:Number 5(2014)
• Page Start: 430
• Page End: 438
• Publication Date: 2014-01-23
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.6795
• Languages: English
• ISSNs: 0951-4198

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="rcm6795-sec-0001" sec-type="section"> <title>RATIONALE</title> <p>For mass analysis, linear quadrupole ion traps operate with dipolar excitation of ions for either axial or radial ejection. There have been comparatively few computer simulations of this process. We introduce a new concept, the excitation contour, <italic>S</italic>(<italic>q</italic>), the fraction of the excited ions that reach the trap electrodes when trapped at <italic>q</italic> values near that corresponding to the excitation frequency.</p> </sec> <sec id="rcm6795-sec-0002" sec-type="section"> <title>METHODS</title> <p>Ion trajectory calculations are used to calculate <italic>S</italic>(<italic>q</italic>). Ions are given Gaussian distributions of initial positions in <italic>x</italic> and <italic>y</italic>, and thermal initial velocity distributions. To model gas damping, a drag force is added to the equations of motion. The effects of the initial conditions, ejection Mathieu parameter <italic>q</italic>, scan speed, excitation voltage and collisional damping, are modeled.</p> </sec> <sec id="rcm6795-sec-0003" sec-type="section"> <title>RESULTS</title> <p>We find that, with no buffer gas, the mass resolution is mostly determined by the excitation time and is given by <alternatives><inline-graphic mimetype="image" xlink:href="ark:/27927/pgg4sqdbf7k" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math display="inline" overflow="scroll" altimg="urn:x-wiley:09514198:media:rcm6795:rcm6795-math-0001" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>R</mml:mi><mml:mo>~</mml:mo><mml:mfrac><mml:mi mathvariant="italic">dβ</mml:mi><mml:mi mathvariant="italic">dq</mml:mi></mml:mfrac><mml:mi mathvariant="italic">qn</mml:mi></mml:mrow></mml:math></alternatives>, where <italic>β</italic>(<italic>q</italic>) determines the oscillation frequency, and <italic>n</italic> is the number of cycles of the trapping radio frequency during the excitation or ejection time. The highest resolution at a given scan speed is reached with the lowest excitation amplitude that gives ejection. The addition of a buffer gas can increase the mass resolution. The simulation results are in broad agreement with experiments.</p> </sec> <sec id="rcm6795-sec-0004" sec-type="section"> <title>CONCLUSIONS</title> <p>The excitation contour, <italic>S</italic>(<italic>q</italic>), introduced here, is a useful tool for studying the ejection process. The excitation strength, excitation time and buffer gas pressure interact in a complex way but, when set properly, a mass resolution <italic>R</italic><sub>0.5</sub> of at least 10, 000 can be obtained at a mass‐to‐charge ratio of 609. Copyright © 2014 John Wiley & Sons, Ltd.</p> </sec> </abstract>