Ion-Molecular Derivatization Reactions of Alcohols in a “Direct Analysis in Real Time” (DART) Mass Spectrometer: 4-N,N-Dimethylaminopyridine as a New Efficient Reagent

Gas-phase on-line derivatization in the ion source of a DART mass spectrometer is a new approach to the efficient detection of alcohols in complex matrices. It does not require any special sample handling; it is based just on mixing an alcohol with a nitrogen-containing compound with high proton affinity. The resulting N-alkyl-derivatized cations appear in DART spectra as very characteristic and highly intense signals. In addition to the earlier used pyridine and quinoline, we propose a new reagent, 4-N,N-dimethylaminopyridine (4-DMAP), having a higher proton affinity. It is shown that DART mass spectra recorded for alcohols in the presence of an equimolar mixture of pyridine and 4-DMAP reveal peaks that are mainly due to the 4-DMAP quaternization cation. This indicates a highly competitive ability of this reagent to get protonated and then predominantly participate in ion-molecular reactions with alcohols under study. It is suggested that 4-DMAP provides high sensitivity in the analysis of aliphatic and alicyclic primary and secondary alcohols.