Influence of Gas Impurities on LC/MS Electrospray Spectra Background Noise

LC/MS technique requires a source compressed gases. The needed amount could be quite significant. Currently the most common source is a gas generator which can deliver nitrogen or dried air needed for source and or collision cell. The purity of the generated gas can have a significant effect on the appearance of false-positive signals in the mass spectrum. The standard N2 membrane is capable of passing through a range of environmental pollutants, including volatile organic compounds (VOCs). Carbon filters are commonly used to improve the quality of gas, however their capacity is limited and their selectivity towards different compounds may differ. The purpose of the research is to demonstrate that dedicated VOC filter installed on ZA FID Air (LNI) generators are more effective at removing these types of impurities.
To evaluate the impact of ZA FID Air generator on electrospray ion spectrum certain modifications were done on an existing LC-MS/MS system. ZA FID Air (LNI) with catalytic oven was added between MS system and gas generator to purify both N2 (CUR, CAD) and dried air (GS1, GS2). The modification allows for dynamic switching between standard line and bypass with the ZA generator. In all experiments, purified and non-purified gases were compared under a variety of ion source and scan conditions (Q1/Q3 scan, SIM, MRM).
According to a preliminary analysis, the number of false positive signals appearing in the ion source is reduced in case of the using the zero air generator with catalytic oven in the gas line, just before the mass spectrometer inlet. In cases of Masdiag laboratory the main interference signal which can be observed in the ESI positive full scan spectra, has m/z 121 and 131.
The reduction in background was more evident in the positive ion mode than in the negative ion mode. As a result of the specificity of the scan, the reduction in background noise was also correlated with the scan mode.