Ion/molecule reactions provide new evidence for the structure and origin of [C3H4N](+) from acetonitrile chemical ionization plasma

Ion/molecule reactions leading to formation of the diagnostically useful [C 3H4N](+) ion (m/z 54), from acetonitrile CI plasma, have been studied using a tandem quadrupole mass spectrometer, Evidence is presented to demonstrat e that [C3H4N](+) is produced from an ion/molecule reaction between [C2H2N] (+) (m/z 40) and neutral acetonitrile, via a [C4H5N2](+) (m/z 81) intermedi ate. Loss of HCN, where the H atom arises from neutral acetonitrile and the CN group from [C2H2N](+) (m/z 40), leads to the production of [C3H4N](+). (m/z 54), These results are consistent with a proposed concerted eliminatio n of HCN, generating m/z 54 as a methylene vinylidene ammonium ion. Copyrig ht (C) 1999 John Wiley & Sons, Ltd.