The reactions of gas-phase ions with neutral molecules in mass spectrometry were investigated. These reactions are rare, due to high vacuum conditions and the high purity of collision gases. The ions of interest originated from the dissociation of thiotetronic acids (TA) and N-Nitrosamines (NDAA). Using soft MS, the structure and properties of TAs were determined. They formed ketene ions which then reacted with water in the collision cell. NDAAs were analysed using sequential tandem MS. The CID products parallel the metabolites produced in biological systems. The size of the aliphatic group determined the alkylating potential of the nitrosamine. The comparison of spectral intensities between isotopically unlabelled NDPA and isotopically labelled NDPA-d14 helped to determine the protonation of diazoic acids is the rate limiting step in the dissociation of diazoic. The addition of water in these dissociation pathways provides better understanding of ion-molecule reactions in MS.