Ion–molecule reactions of trimethylborate allow the mass spectrometric identification and counting of functional groups in protonated bifunctional oxygen-containing compounds and polyols

Abstract

A mass spectrometric method has been developed for the identification of functional groups in unknown bifunctional oxygen-containing compounds and for the identification and counting of the hydroxyl groups in polyols. This method utilizes gas-phase ion–molecule reactions of protonated analytes with neutral trimethylborate (TMB) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The diagnostic reaction sequence involves proton abstraction from the protonated analyte by TMB, followed by the addition of the analyte to TMB and elimination of methanol. The functional groups in bifunctional oxygen-containing compounds are identified based on the total number of TMB molecules that have added to the protonated analyte and/or the number of methanol molecules lost, or by sustained off-resonance irradiation collision-activated dissociation (SORI-CAD) of the reaction products. The number of hydroxyl groups in polyols is revealed by the number of methanol molecules lost during their reactions with TMB. Reactions of protonated carboxylic acids with TMB also lead to elimination of a methanol molecule. However, carboxylic acids can be differentiated from the isomeric hydroxyketones based on the loss of HO-B(OCH 3) 2 upon SORI-CAD of the reaction product. Reactions of protonated amides with TMB also lead to elimination of a methanol molecule. However, amides can be differentiated from bifunctional oxygen-containing compounds based on the loss of O B R from the reaction product upon SORI-CAD. Protonated amines do not react with TMB.