Mass spectral discrimination between monoenoic and cyclopropanoid, and between normal, iso, and anteiso fatty acid methyl esters.

Measurement of the ratio of the intensity of the parent molecular ion to that of the parent molecular ion minus 32 (the mass of methanol) can distinguish between monoenoic and cyclopropanoid fatty acid methyl esters with the same carbon number. A similar technique can be used to distinguish between isomeric normal, iso, and anteiso fatty acid methyl esters.