Study on Measurement of CxHy Outgassing Rate Based on the Correction for Quadrupole Mass Spectrometer Mass Discrimination

The hydrocarbon species (CxHy) released by the material have a significant impact on the performance and life of precision instruments. The quadrupole mass spectrometer (QMS) is one of the most established and widely used partial outgassing rate measurement instruments. However, a potential issue with QMS is the high-mass discrimination effect, wherein ions with lower m/z values are transmitted more efficiently than those with higher m/z values. It also leads to a reduction in the sensitivity of QMS when measuring CxHy with higher m/z values. To address this problem, this paper proposes a method using dodecane to correct the high-mass discrimination effect of QMS. To ensure stable injection of dodecane gas and maintain the pressure within the working conditions of QMS, a dedicated sampling device for dodecane gas is designed. Furthermore, to verify the effectiveness of the proposed method, the high-mass discrimination effect of two quadrupole mass spectrometers of the model QMG250 M2 was corrected, and the CxHy outgassing rate of polytetrafluoroethylene (PTFE) was measured by continuous expansion method. The results demonstrate that the method proposed in this paper can effectively reduce the impact of the high-mass discrimination effect on the measurement of CxHy with higher m/z values, while significantly increasing the outgassing rate of CxHy from PTFE.