Application of isobutane and ammonia chemical ionization mass spectrometry for the analysis of volatile terpene alcohols and esters

Abstract

AbstractThe ionization and fragmentation behaviour of mono‐and sesqui‐terpene alcohols and esters in CI mass spectrometry was investigated. The reagent gases used were isobutane and ammonia. Isobutane yields the species [MH]+ as the quasimolecular ions which, however, are extremely small for many of the investigated compounds. Ammonia gives intense [M + 18]+ quasimolecular adduct ions. The assignment of the molecular mass is more reliable in ammonia than in isobutane CI. Alcohols and esters form characteristic fragment ions. Alcohols show the mass difference of 18 mass units and esters display the difference of the respective acid in the patterns of the CI spectra. This fact enables one to distinguish the classes of the terpene alcohols and esters by means of CI. Particular compounds, as well as cis/trans and stereoisomers, can be differentiated by their ion patterns. CI spectra are strongly dependent on experimental conditions. High ion source temperature favours fragmentation diminishing the relative intensity of the quasimolecular ion. High ammonia reagent gas pressure reduces the relative intensities of fragment ions enhancing the relative abundancies of the quasimolecular adduct ions.Mass spectrometry Chemical ionization (CI) Isobutane reagent gas Ammonia reagent gas Monoterpenes Sesquiterpenes Alcohols Esters.