Application of APPI for Reduction of Background Signal Observed in SFC-MS with Columns Utilizing Ethyl-Pyridine and Other Basic Stationary Phases

摘要

High mass spectral background under SFC-ESI conditions can be attributed to the ionization of column bleed components. (1) The characterization of the column-related components indicate that they are products formed by cleavage of the stationary phase by the alcohols used as CO_(2) modifiers. (2) The intensity of background signal scales with the expected reactivity of the alcohol used (methanol > ethanol > isopropanol). APPI ionization can successfully decrease the column background observed. (1) This decrease results in better sensitivity and higher confidence in the detection of low level unknown impurities. (2) The success of this approach depends upon the selective ionization of the analytes in the presence of basic stationary phase-related material in the mobile phase. (3) For analytes that require ESI for detection silica is the preferred stationary phase for lowest chemical background.