Molecular Ion M^+· Formation under Fast-atom Bombardment Conditions Using Protic and Aprotic Liquid Matrices

Abstract

Positive ion fast-atom bombardment (FAB) mass spectra of some benzofuran or dihydrobenzopyran derivatives gave intense and predominant molecular ion M^+· peaks even when a protic liquid matrix DTT/TG13, i.e., 1 : 3 (v/v) mixture of dithiothreitol (DTT) and thioglycerol (TG), is used. The above spectra were compared with the usual FAB mass spectra, showing a predominant protonated molecule MH⁺ peak, of the compounds containing such significant proton acceptors as carbonyl and carboxyl group. It was suggested that preferential formtion of M^+· to MH⁺ ions is due to the structure of above derivatives, except for trolox (4), which do not contain the significant proton acceptor.
Furthermore, it was observed that the change of matrix from DTT/TG 13 to m-nitrobenzyl alcohol (m-NBA) increases the ratio of intensties I (M^+·)/I(MH⁺) as a matrix effect.