Use of Trimethyl Borate as a Chemical Ionization Reagent for the Analysis of Biologically Active Molecules

The use of dimethoxyborinium ion as a chemical ionization reagent for biologically active organic molecules containing functional groups of Lewis basicity was investigated. Both the efficiency of borinium adduct formation and the degree of structural information obtained from collisionally activated dissociation (CAD) spectra of the adducts were evaluated relative to that of the protonated molecules. The borinium ion adducts include two main species: [M+73]+, which corresponds to the analyte bound to one dimethoxy borinium ion, and the [M+41]+ species, which corresponds to the [M+73]+ adduct after a loss of methanol. CAD of these dimethoxyborinium ion adducts often yields a large number of fragments. While fragments may not occur in high yield, they may serve as highly effective fingerprints which are useful for compound identification. Mechanistic explanations for some of the predominant fragments are proposed in an attempt to rationalize the structures of the borinium ion adducts.