Determination of the double bond position in functionalized monoenes by chemical ionization ion-trap mass spectrometry using acetonitrile as a reagent gas

Acetonitrile may be used as a chemical ionization reagent gas in ion-trap mass spectrometry for the location of double bonds in functionalized long-chain monoenes. [C3H4N]+, derived from acetonitrile, reacts with carbon–carbon double bonds, generating one or a pair of fragment ions characteristic of the position of the double bond in the chain. Tolerance of a range of functional groups is achieved by isolating [C3H4N]+ from the other acetonitrile ions before reaction with the alkene. Under these conditions, competing processes such as protonation are minimized, and a different mode of fragmentation from that previously observed with unfunctionalized alkenes11 is obtained. The technique is highly sensitive (<0.5 ng), allowing its use in the identification of insect pheromones.