Quadrupole Ion Optics and Series Oscillating Electronics System

Quadrupoles are essential components in mass spectrometry instruments, such as liquid chromatography mass spectrometry (LC/MS), triple quadrupole mass spectrometry (QQQ) and quadrupole time-of-flight mass spectrometry (Q TOF), and similar domestic instruments are severely lacked in China. At present, the domestic enthusiasm for the development of mass spectrometers is increasing, and the recommendations and slogans of “Making Chinese Mass Spectrometers” are put forward, which has been highly recognized and responded by the government and research personnel. This review focused on technical principles for quadrupole ion optics and electricity based on many years of author’s experience in the development of the core technology principles of mass spectrometry. Firstly, the theoretical basis of quadrupoles were introduced in brief. Next, the importance of mechanical accuracy in quadrupole processing and assembly were introduced in order to improve quadrupole resolution, including the effect of rod size selection on quadrupole radio frequency (RF) voltage control. Finally, we highlighted the quadrupole electronics with a serial oscillating model, and its impedance matching which played a key role in quadrupole performance. The core technical principle of the series RF oscillating circuit is that the two-stage series oscillation is applied. Two-stage voltage amplification can step up the voltage to the required amplitude in a relatively easy manner. Besides, the two-stage impedance matching can be realized between the low-resistance oscillation source and the high-resistance quadrupole load smoothly. The series oscillation uses a symmetrical RF oscillation source. The low internal resistance RF voltage source provides the primary RF voltage, which is boosted to the RF medium voltage through the first-stage series LC oscillation and obtains a higher load impedance. The RF medium voltage is coupled by a capacitance to the second stage series LC oscillation, boosted again to the required RF amplitude and matched to the impedance of quadrupole. RF radiation shielding is also an important part of the series oscillation process, which determines the quality of series oscillation. Series oscillations make it easier to obtain high RF voltages, and possible to analyze large mass molecules for quadrupoles.