Ammonia chemical ionization mass spectrometry of substituted phenylpropanoids and phenylalkyl phenyl ethers

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AbstractThe ammonia chemical ionization (NH3/CI) spectra of phenylpropanoids and substituted phenylalkyl phenyl ethers containing α‐hydroxy or α‐carbonyl functional groups are discussed. Fragmentation reactions which occur in the temperature range 180–450°C are examined to model pyrolysis mass spectrometric experiments of lignin. Hydroxycinnamyl alcohols and α‐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 α‐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 [15N] ammonia (15NH3) 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.