PREPARATION OF FATTY-ACID METHYL ESTERS FOR GAS-CHROMATOGRAPHIC ANALYSIS OF LIPIDS IN BIOLOGICAL-MATERIALS

Theoretically, preparation of fatty acid methyl esters (FAMEs) deals w ith reversible chemical reactions in a complex system. Methodologicall y, there are numerous ways, generally characterized by the type of cat alysts used and steps involved. Although there are more than a half do zen common catalysts, the majority fall into either acidic (HCl, H2SO4 and BF3) or alkaline types (NaOCH3, KOH and NaOH), with each having i ts own catalytic capability and application limitations. In terms of s teps, many conventional methods, including those officially recognized , consist of drying, digestion, extraction, purification, alkaline hyd rolysis, transmethylation/methylation and post-reaction work-up. Altho ugh these methods are capable of providing reliable estimates if some precautions are taken, they are cumbersome, time-consuming and cost-in efficient, A new approach has been to transmethylate lipids in situ, D ue to its simplicity, high sensitivity, comparable reliability and cap ability to determine total fatty acids, the method of direct transmeth ylation is finding a unique place in lipid determination. Regardless o f which method is used, quantitative methylation requires chemists to take precautions at every step involved, particularly during FAME form ation and subsequent recovery steps. Evidently, there is an urgent nee d for more systematic studies, guided by the chemical principle of rea ctions involved and physicochemical properties of regents and end prod ucts, into factors affecting these steps. Hopefully, this will lead to an improved method, which measures lipid composition in biological ma terials not only with high accuracy but also with high efficiency and minimum costs.