The selectivity and sensitivity of methanol chemical ionization mass spectrometry was studied for selected heteroatom-containing compounds chosen as representative of trace contaminants in middle distillate fuels. At high methanol pressures, the selectivity for these species, relative to n- butylbenzene, was found to improve by factors of 2–4 over that observed with methane chemical ionization. At lower methanol pressures, the sensitivities for these components exhibited a two- to eleven-fold increase over that observed with methane.
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