The differentiation of isomers and their identification constitute the subject of continuous interest since different isomers can have widely varying pharmacological and toxicological properties and environmental impact. Mass spectrometry (MS) is a powerful technique for the characterization of isomeric compounds. MS offers several advantages including high sensitivity and capability to perform analysis without isolating and purifying the mixture components. In same cases, chemical ionization (CI) combined with multi-stage collision-induced dissociation (CID) has provided differences in fragmentation useful for the differentiation of isomeric analytes. The α-phenylvinyl cation (α-PVC) m/z 103, generated by chemical ionization (methanol) from phenylacetilene, reacts with neutral aromatic compounds to form the characteristic species: [M + 103]+ adduct ions and the trans-vinylating product ions [M + 25]+, which correspond to [M + 103]+ adduct after the loss of benzene (Figure 1).[1] In a previous study, it was demonstrated that CID experiments on the [M + 103]+ adduct ions, using a quadruple ion-trap mass spectrometer, was effective for the differentiation of isomeric naturally-occurring phenols.[2] However, the fragmentation behaviour of the [M + 25]+ fragment ions was not investigated. This study illustrates the effectiveness of CI (α-PVC) for isomer differentiation based on the CID mass spectra of the [M + 25]+ fragment ions. In particularly, we focused our attention on certain class of low mass isomeric compounds where conventional EI-MS (/MS) does not work successfully. Substituted isomeric phenols, i.e. methoxyphenols and dihydroxybenzenes, have been chosen as model compounds as they are widely used in many field, such us cosmetic, tanning, dye, chemical and pharmaceutical industries, and, as a consequence, they are often encountered as environmental pollutants. Key mechanistic details were tentatively proposed based on MSn experiments carried out on the adduct ions using labeled derivatives when synthetically accessible or commercially available.
FORMATION OF THE [M+ 25]+ FRAGMENT ION IN THE CI (PHENYLACETYLENE) MASS SPECTRA OF AROMATIC COMPOUNDS: A USEFUL PRECURSOR ION FOR ISOMERIC DIFFERENTIATION
BEGALA, MICHELA
2015-01-01
Abstract
The differentiation of isomers and their identification constitute the subject of continuous interest since different isomers can have widely varying pharmacological and toxicological properties and environmental impact. Mass spectrometry (MS) is a powerful technique for the characterization of isomeric compounds. MS offers several advantages including high sensitivity and capability to perform analysis without isolating and purifying the mixture components. In same cases, chemical ionization (CI) combined with multi-stage collision-induced dissociation (CID) has provided differences in fragmentation useful for the differentiation of isomeric analytes. The α-phenylvinyl cation (α-PVC) m/z 103, generated by chemical ionization (methanol) from phenylacetilene, reacts with neutral aromatic compounds to form the characteristic species: [M + 103]+ adduct ions and the trans-vinylating product ions [M + 25]+, which correspond to [M + 103]+ adduct after the loss of benzene (Figure 1).[1] In a previous study, it was demonstrated that CID experiments on the [M + 103]+ adduct ions, using a quadruple ion-trap mass spectrometer, was effective for the differentiation of isomeric naturally-occurring phenols.[2] However, the fragmentation behaviour of the [M + 25]+ fragment ions was not investigated. This study illustrates the effectiveness of CI (α-PVC) for isomer differentiation based on the CID mass spectra of the [M + 25]+ fragment ions. In particularly, we focused our attention on certain class of low mass isomeric compounds where conventional EI-MS (/MS) does not work successfully. Substituted isomeric phenols, i.e. methoxyphenols and dihydroxybenzenes, have been chosen as model compounds as they are widely used in many field, such us cosmetic, tanning, dye, chemical and pharmaceutical industries, and, as a consequence, they are often encountered as environmental pollutants. Key mechanistic details were tentatively proposed based on MSn experiments carried out on the adduct ions using labeled derivatives when synthetically accessible or commercially available.
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