Analysis of triacylglycerols by silver‐ion high‐performance liquid chromatography‐atmospheric pressure chemical ionization mass spectrometry

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Abstract
Triacylglycerols of the seed oils rich in α‐ and/or γ‐linolenic acid moieties were separated by silver‐ion high‐performance liquid chromatography (HPLC) followed by on‐line atmospheric pressure chemical ionization‐mass spectrometric (APCI‐MS) detection. Mass spectra of most triacylglycerols exhibited abundant [M + H]+ and [M − RCO2]+ ions, which defined the molecular weight and the molecular association of fatty acyl residues of a triacylglycerol, respectively. Silver ions formed weaker complexes with triacylglycerols containing γ‐linolenic acid than with those containing α‐linolenic acid, i.e., the elution order of molecules wasXYTγ>XYTα’,XTγTα>XTαTα>, andTγTγTγ>TγTγTα>TγTαTα>TαTαTα, whereTα=α‐linolenic acid,Tγ=γ‐linolenic acid, andX, Y=fatty acids different from linolenic acid. Furthermore, silver‐ion HPLC resulted in partial separation within equally unsaturated triacylglycerols according to differences in the combined number of acyl carbons. Regioisomeric forms of triacylglycerols were not determined from the seed oil samples, although differences were measured with reference compounds in the relative abundances of [M − RCO2]+ ions formed by a loss of a fatty acyl residue from thesn‐2 position and thesn‐1/3 positions. Silverion HPLC/APCI‐MS provided valuable information for structure elucidation of seed oil triacylglycerols: 43 molecular species were identified from cloudberry seed oil, 39 from evening primrose oil, 79 from borage oil, 44 from alpine currant, and 56 from black currant seed oils. The quantitation requires to be studied further, especially in those cases where several molecular weight species of triacylglycerols eluted in a single chromatographic peak.