title: [The effect of alkalinity of methylation reagent on isomerization and degradation of polyunsaturated fatty acids with pyrolysis gas chromatography].
abstract: Simultaneous pyrolysis and methylation gas chromatography (SPM-GC) is a fast analytical method which was developed in recent years. However, the strong alkalinity of tetramethylammonium hydroxide (TMAH) may result in the isomerization and degradation of polyunsaturated fatty acids in oils and fats during analysis. This paper describes the application of SPM-GC to polyunsaturated fatty acids in soybean oil and the isomerization and degradation may be prevented by choosing the optimum proportion of TMAH to methanol which is 1:50 (pH 8.8). With this chosen optimum proportion there were no detectable isomerized and degraded peaks in the chromatograms. Pyrograms were obtained by interfacing a Curie-point pyrolyser to a Shimadzu GC-14A gas chromatograph equipped with a flame ionisation detector. A capillary column (FFAP) was used. All of the pyrolysis products were identified by mass spectrometry which was carried out with a Varian 3400 gas chromatograph interfaced to a Finnigan SSQ 710 mass spectrometer using electron impact ionisation (70 eV). This method is simpler and more convenient than both the methods "neutralization of acid" and "simultaneous injection of the sample and a short chain fatty acid methylester" reported in the previous papers.
authors.affiliation: Liaoning Criminal Science and Technology Institute, Shenyang, 110032.
authors.forename: J
authors.initials: J
authors.lastname: Ding
authors.forename: W
authors.initials: W
authors.lastname: Jing
authors.forename: T
authors.initials: T
authors.lastname: Zou
authors.forename: M
authors.initials: M
authors.lastname: Song
authors.forename: X
authors.initials: X
authors.lastname: Yu
authors.forename: C
authors.initials: C
authors.lastname: Fan
mesh_terms: D002849:Chromatography, Gas / Q000295:instrumentation / Q000379:methods*; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D007536:Isomerism; D008745:Methylation; D013024:Soybean Oil / Q000032:analysis*
chemical_list: D005231:Fatty Acids, Unsaturated; D013024:Soybean Oil