Characterization and Improvement of Signal Drift Associated with Electron Ionization Quadrupole Mass Spectrometry

摘要

Quadrupole mass spectrometry with electron ionizationn(EI-QMS) is a very popular detection technique in combinationnwith gas chromatography. It is deployed for thenanalysis of volatile and semivolatile analytes in manynindustry domains. Although a very important factor fornquantitative analysis, little is known about the stability ofnion source performance. Only a few papers and patentsnreport possible signal instabilities due to sample adsorption,ndegradation, or insulating deposits on the hot stainlessnsteel surface of the ion source. In this study, anconventional stainless steel ion source was used toninvestigate possible signal drifts. It was observed that thenEI-QMS instrument indeed suffered from continuousnsignal instability. It was found that the key parts whichnare responsible for the signal instabilities are those thatnregulate the ion beam toward the mass analyzer: thenrepeller, exit plate, and focusing lenses. The voltage of thenrepeller was found to have a major influence on the signalnstability. The surface of the repeller, exit plate, andnfocusing lenses was modified by applying a gold coating.nIt was demonstrated that the signal stability of the MSndramatically improved when using the gold-coated parts.nThe contribution of each part to the stability improvementnwas quantitatively determined and compared with thenstandard stainless steel source performance. It was assumednthat the signal drift observed with the stainlessnsteel EI source originated from charge buildup on thensurfaces. This hypothesis was supported by softwarensimulations.