Abstract
On the gas chromatography of fatty acid methyl esters prepared from trace amounts of lipids, the accurate analysis of the esters is sometimes interfered with phthalates which are eluted from various materials used in the course of sample preparations for gas chromatography. We devised a simple method for removal of the contaminative phthalates from a sample for gas chromatography.
The method was comprised of a sequence of methanolysis and thin-layer chromatographic separation, and this simple combination technique was effectively applied to gas chromatographic microanalysis of fatty acid methyl esters which were contaminated with a wide variety of phthalates. By re-methanolysis of fatty acid methyl esters containing phthalates with 0.5% (wt/vol) sodium methoxide at 80°C for 30 min, the phthalates were converted into dimethyl phthalate and small amounts of heterogeneous phthalates containing one methyl group, but the fatty acid esters were unchanged during the treatment. The resulting mixture was spotted on thin-layer plate which was cleaned up with ether before use, and developed with a solvent mixture of hexane-ether-acetic acid (80/20/1, vol/vol/vol). The fatty acid methyl esters were separated on the plate from the contaminative phthalates, by taking advantage of higher Rf values of the fatty acid esters than those of the methanolysis products from the contaminants. The purified fatty acid methyl esters could be re-analyzed by gas chromatography without any interferences. This method had no influence on the fatty acid methyl esters to be analyzed.
