Application of capillary supercritical fluid chromatography–double focusing mass spectrometry under negative ion chemical ionization conditions

Abstract

AbstractThe application of mass spectrometry in the negative ion mode with capillary column supercritical fluid chromatography is described. The supercritical fluid chromatography mobile phase (CO2) was used as the primary reagent gas to generate thermalized electrons and reagent anions (such as O− and CO2−). When trace amounts of CH4 or NH3 gas were also introduced into the chemical ionization source, the mass spectrometer sensitivity was increased. Detection limits (S/N = 5) for heptachlor were determined to be 20 pg and 200 fg for full scan and selected ion monitoring modes, respectively. Mass spectra of a cyclic peptide, valinomycin, obtained with these mixed reagents (CH4 + CO2 and NH3 + CO2) gave the molecular anion at m/z 1110 as the most abundant ion and additional fragment ions that yielded peptide sequence information.