Development of RF-only Quadrupole Ion Guide for Transmission of Low Mass-to-Charge Ratio Ions

The ion guide system is an important part of the mass spectrometer, which main function is to efficiently transfer ions to the mass analyzer. In this work, a radio frequency quadrupole ion guide device for proton transfer reaction time-of-flight mass spectrometry (PTR-TOF MS) was developed and the quadrupole length was 80 mm, the rod radius was 2.6 mm, and the inscribed circle radius was 2.25 mm. This device realized focusing and transmission of volatile organic compounds (VOCs) with low mass-to-charge ratio. The movement of ions in the RF-only quadrupole device was simulated by SIMION 8.1 ion optical simulation software. The working conditions of the device, such as pressure, frequency and voltage amplitude, were tested on the home-built test platform. The results showed that the simulation and test had good consistency. The working pressure, frequency and amplitude of voltage were optimized to be 0.2-0.3 Pa, 3-4 MHz and about 500 V, respectively. The transmission efficiency of low mass-to-charge ratio VOCs (less than m/z 100) ions such as acetone and toluene was close to 76% with ion beam diameter no more than 0.7 mm. The device has the advantages of simple structure, low cost and high transmission efficiency, and which will be expected to be used in the PTR-TOF MS system.