Solid-phase extraction and liquid chromatography--mass spectrometry for the determination of free fatty acids in shellfish

A novel analytical protocol for the determination of free fatty acids (FFAs; saturated, monounsaturated and polyunsaturated) in shellfish using electrospray ionisation and liquid chromatography-mass spectrometry (LC-MS) is described. Total lipids were extracted from four commercially important shellfish species using chloroform-methanol in a modification of the traditionally used Bligh and Dyer method. FFAs were recovered from lipidic shellfish extracts by solid-phase extraction (SPE) on an aminopropyl-silica column using a 98:2 v/v diethyl ether (DEE)-acetic acid solution. Ether extracts containing the FFAs were evaporated and reconstituted in 70:30 v/v methanol-chloroform before analysis by LC-MS. The limits of quantification (LOQs) of the method ranged from 60 to 560 microgg(-1) wet weight depending on the different FFAs determined with selected ion monitoring (SIM). Results demonstrate that LC-MS is well suited for identification and quantification of FFAs in shellfish and negates the use of sample derivatisation required in gas chromatographic analysis.