Gas phase reactions are of fundamental interest in smoke chemistry. Many types of reactions and decompositions have been characterized. However, one type of reaction, the charge transfer process, is very difficult to characterize by conventional means. Methods have been developed using a four sector tandem mass spectrometer for chemical characterization of charge-reversal charge transfer reaction products. This is accomplished by operating two of the sectors of the instrument in the negative ion mode and the other two sectors of the instrument in the positive ion mode with inert gas collision at the interface to facilitate charge transfer. For example if a negatively charged ion generated and selected in MS I is collisionally activated at the interface and the products are analysed with MS II in the positive ion mode, then only chemical species generated in charge-reversal charge transfer processes of the original parent anion are identified. This technique has been applied to fundamental studies of model compounds including fatty acids, solanesol, sugars and humectants.