Development of charge detector rectilinear ion trap (CD-RIT) mass spectrometer
Avinash A. Patil1*, Szu-Wei Chou1, Chen-Wei Lee1, Wen-Ping Peng1
1Physics, National Dong Hwa university, Hualien, Taiwan
* presenting author:Avinash Adhikrao Patil,

This study presents the development of charge detector rectilinear ion trap mass spectrometer (CD-RIT) for the analysis of high mass MALDI ions. Conventional linear ion trap mass analyzer employed secondary electron detector to detect ions. However, to trap high mass ions, buffer gas (>5 mtorr) must be raised to quench the kinetic energy of ions by collision cooling, which limits the voltage applied on dynode assembly (<10KV) of secondary electron detector and declines secondary ion yield of high mass ions. To improve the detection of high mass ion, we developed a charge detector which detects image charge of molecular ions and the detection efficiency is independent of secondary electron yield. To employ charge dtetector, it is inevitably to pick up strong rf field and thus saturates the charge detector. To remove the rf interference noise, we adopted a copper cover plate with a guarding mesh which covered charge detector to reduce the induced strong rf field generated from RIT and developed orthogonal wavelet packet decomposition (OWPD) method to analyze all rf noise components and remove rf field interference completely. Thus strong rf interference could be removed
The performance of CD-RIT MS is tested with mass ranging from hundreds of Dalton ( C60 and CsI clusters) to kilo-Dalton ( Ubiquitin , cytochrome C) and also compared with a secondary electron detector results. The fast response time (700┬Ásec) of charge detector able to separates the two nearest m/z ion signals more efficiently than secondary electron. This improves the resolution of signals 40% better in charge detector than secondary electron detector. We also found the ratio of the signal intensities of secondary electron detector and charge detector decreases as mass increases. This indicates the charge detector is suitable for high mass detection than a secondary electron detector.
The study concludes that the charge detector can be successfully coupled with a rectilinear ion trap and CD-RIT MS is able to detect molecular ions with ion a detection limit of 1000 ions. The charge detector can acquire better ion signal as compared to a secondary electron detector as mass is increasing.

Keywords: Mass spectrometry, Rectilinear ion trap, Charge detector, Secondary electron detector, Proteins