Identification of Carbon-Carbon Double Bond Stereochemistry in Unsaturated Fatty Acids by Charge-Remote Fragmentation of Fixed-Charge Derivatives.

Separation and identification of fatty acid (FA) isomers in biological samples represents a challenging problem for lipid chemists. Notably, FA regio- and stereo-isomers differing in the location or (cis/trans) geometry of carbon-carbon double bonds are often incompletely separated and ambiguously assigned in conventional chromatography-mass spectrometry analyses. To address this challenge, FAs have been derivatized with the charge-switch derivatization reagents N-methyl-pyridinium-3-methanamine and N-(4-aminomethylphenyl)pyridinium and subjected to reversed-phase liquid chromatography-tandem mass spectrometry. Charge-remote fragmentation of the fixed-charge derivatives leads to characteristic product ions arising from dissociation at allylic positions that enable assignment of position(s) of unsaturation, while a newly discovered dihydrogen neutral loss was found to be dominant for double bonds with cis-stereochemistry. The structure of the [M - 2]+ product ions was probed by gas-phase ozonolysis revealing the presence of two new carbon-carbon bonds on either side of the initial position of unsaturation consistent with an electrocyclic mechanism of 1,4-dihydrogen elimination. Charge-remote fragmentation pathways diagnostic of double bond position and stereochemistry were found to be generalized for FAs of different carbon-chain lengths, double bond positions, and degrees of unsaturation and were effective in the unequivocal assignment of the FA structure in complex mixtures of FA isomers, including bovine milk powder.

A rapid method for the simultaneous quantification of the major tocopherols, carotenoids, free and esterified sterols in canola (Brassica napus) oil using normal phase liquid chromatography.

A normal phase high performance liquid chromatography (HPLC) method was developed to simultaneously quantify several prominent bioactive compounds in canola oil vis. α-tocopherol, γ-tocopherol, δ-tocopherol, ß-carotene, lutein, ß-sitosterol, campesterol and brassicasterol. The use of sequential diode array detection (DAD) and tandem mass spectrometry (MS/MS) allowed direct injection of oils, diluted in hexane without derivatisation or saponification, greatly reducing sample preparation time, and permitting the quantification of both free sterols and intact sterol esters. Further advantages over existing methods included increased analytical selectivity, and a chromatographic run time substantially less than other reported normal phase methods. The HPLC-DAD-MS/MS method was applied to freshly extracted canola oil samples as well as commercially available canola, palm fruit, sunflower and olive oils.