INTERFERENCE EFFECTS CAUSED BY OXIDATION AND REDUCTION PROCESSES IN FAST ATOM BOMBARDMENT MASS-SPECTROMETRY

A detailed study of the molecular ion region of four high mass (800-2600 dalton) compounds (bradykinin, ramoplanin, teicoplanin, A2 component and rifapentin) under fast atom bombardment showed significant deviations from the theoretical isotope pattern of the protonated molecular ion. The differences indicate the presence of various (M ± nH)+ ions (n = 0...5), which suggest oxidation and reduction reactions occuring simultaneously. In the molecular ion region of the monoisotopic spectra the (M + H)+ ion was the most abundant species in each case studied, but represented only 40-85% of all ions. As the samples studied do not contain any easily reducible or very labile groups, this observation seems to be a general phenomenon for high mass compounds. Consequences for using the "isotope" pattern in the determination of elemental formula and using "mean" molecular masses from less than unit resolution spectra are also discussed. © 1990.