Simultaneously improving the resolving power and sensitivity for planar high-field asymmetric waveform ion mobility...

Resolution and sensitivity are two key parameters for describing the performance of high-field asymmetric waveform ion mobility spectrometry (FAIMS). An increase in the resolving power of FAIMS has been realized by adding helium to nitrogen in planar FAIMS, but it comes at the expense of sensitivity.

Here, a new hollow needle-to-ring discharge device integrated on a PCB substrate is used as the ion source for FAIMS. Helium flows from the hollow part of the hollow needle to improve the ionization effect. Nitrogen carries the sample into the ionization chamber and is mixed with helium as the carrier gas.

Under a nitrogen flow rate of 1 L min^-1 , 1.5 L min^-1 , 2 L min^-1 , and 2.5 L min^-1 , adding helium at different flow rates (0.2 L min^-1 , 0.3 L min^-1 , 0.5 L min^-1 , and 1 L min^-1 ) can simultaneously improve the separation ability and sensitivity. Helium and nitrogen with flow rates of 0.2, 0.3, 0.5, and 1 L min^-1 were added to nitrogen (2 L min^-1 ). The separation ability and sensitivity of the mixed gases doped with helium are better than those of nitrogen. The larger the RF voltage amplitude is, the more obvious the improvement in the separation ability when helium is added. However, helium doping has the opposite effect on the sensitivity.

This study provides a new idea and technical means for the application of helium and nitrogen gas mixtures in planar FAIMS. This method can greatly improve the performance of FAIMS.