Tetramethylsilane chemical ionization mass spectrometry of some isomeric unsaturated dicarboxylic acids and esterst

The tetramethylsilane (TMS) chemical ionization (CI) mass spectra of some geometrical isomers of unsaturated dicarboxylic acids, esters and isomeric phthalic acids reveal explicit differences. The (E)-acids show an abundant M + 73 ? CH₄]⁺Ion whereas the (Z)-acids exhibit a strong M + 73 ? H₂O]⁺ ion in their TMS CI spectra. The loss of CH₄ from the adduct of fumaric acid has been confirmed by the study of fumaric acid-d₂ and B/E linked scan studies. In the case of esters, the TMS CI spectra of (E)-isomers contain abundant M + 73]⁺ adduct ions, whereas these are weakly abundant in the TMS CI of the (Z)-isomers.