Study on Hydrolysis Method for Extremely Small Amount of Lipids by Organic Basic Sloution, Tetramethylammonium Hydroxide/Methanol and Capillary Gas Chromatographic Analysis of Fatty Acid Composition Depending on Derivatization Methods
Owing to the destruction and loss of fatty acid in the extraction and hydrolysis process of extremely small lipid sample with inorganic strong basic solution, KOH or NaOH/ethanol, there is a great necessity for a hydrolysis reagent to defend the destruction and enhance the extraction of hydrolyzed fatty acid during the hydrolysis and extraction steps. Tetramethylammonium hydroxide(TMAH)/methanol was employed as alternative. Standard triglycerides were hydrolyzed with 1 M KOH/ethanol and 1 M TMAH/methanol, respectively and fatty acid recoveries were determined in three different derivatives, methyl ester, trimethylsilyl(TMS) and N(O)-tert-butyldimethylsilyl(tBDMSi) derivatives. The recoveries of fatty acids from standard triglycerides with TMAH hydrolysis were higher from 1.3 to 65 times than those of KOH hydrolysis. Fatty acid recoveries from the sample lipids, beef tallow, corn oil and tuna eyeball oil, also showed same results as standard triglycerides. The fatty acid composition of the sample lipids determined by TMAH bydrolysis showed close values with the values from the A.O.A.C. method regardless of derivatizatin methods. But in the case of KOH hydrolysis the fatty acid compositions showed significantly different values among the derivatives and from those of the A.O.A.C. method. In the KOH hydrolysis, the precision of the data obtained form recoveries or compositions of fatty acid were very poor compared to TMAH hydrolysis. In the extraction steps of hydrolyzed fatty acids on the case of KOH hydrolysis, substantial amount of fatty acid were simultaneously removed by the extraction with diethyl ether for removal of nonsuponifiable materials. When the hydrolyzed fatty acids after the extraction of nonsaponifiable materials extracted with hexane, significantly small amount were extracted compared to TMAH hydrolysis. The total amounts of fatty acids recovered from the residues of each layer in the extraction steps, such as diethyl ether layer for the removal of nonsaponifiable materials, hexane layer extracted fatty acids and the water layer remained after extraction of hydrolyzed fatty acids, were significantly higher in the case of TMAH hydrolysis than those of KOH hydrolysis.