AMMONIA CHEMICAL-IONIZATION MASS-SPECTROMETRY OF SUBSTITUTED PHENYLPROPANOIDS AND PHENYLALKYL PHENYL ETHERS

The ammonia chemical ionization (NH3/CI) spectra of phenylpropanoids and substituted phenylalkyl phenyl ethers containing alpha-hydroxy or alpha-carbonyl functional groups are discussed. Fragmentation reactions which occur in the temperature range 180-450 degrees C are examined to model pyrolysis mass spectrometric experiments of lignin. Hydroxycinnamyl alcohols and a-hydroxy phenylalkyl phenyl ethers show abundant [M + H - H2O](+) elimination ions and to a lesser extent [M + NH4 - H2O](+) substitution ions while hydroxycinnamic acids and alpha-carbonyl phenylalkyl phenyl ethers show predominantly [M + H](+) and [M + NH4](+) ions. The interpretation of functional group information is facilitated by using trideuterioammonia (ND3) and [N-15]ammonia ((NH3)-N-15) as reagent gases. Labile hydrogens undergo essentially complete exchange upon ND3/CI and the number of hydroxyl functional groups is readily determined by comparison of the [M + NH4](+) and [M - nH + nD + ND4](+) adduct ions. Incomplete H-D exchange is observed for enolizable and aromatic protons.