Acetone chemical ionization studies. Acetone chemical ionization studies-IX: Amino acids and nucleobases

Abstract

Acetone chemical ionization mass spectra of 16 natural -amino acids and 5 free nucleobases show characteristic ions corresponding to [M + H]⁺, [M + 43]⁺ and [M + 59]⁺ ions. The proton affinities of the substrates are found to control the formation of the above ions. The site of acetylation of amino acids under acetone chemical ionization conditions has been studied by the comparison of collision induced dissociation mass spectra of [M + 43]⁺ ions from the amino acids with those of [M + H]⁺ ions from the corresponding N-acetyl amino acids, generated under both methane chemical ionization and liquid secondary ion mass spectrometric conditions. It is concluded that the site of acetylation depends on the nature of the functional groups present. The structure of the [M + 43]⁺ ions of nucleobases is indicated to be an ion-neutral complex between the protonated nucleboase and ketene.