GC/MS determination of fatty acid picolinyl esters by direct Curie-point pyrolysis of whole bacterial cells

Abstract

A single-step method suitable for cellular fatty acid derivatization to picolinyl esters with the use of a pyrolyzer as a thermochemical micro-reactor was developed for whole bacterial cells. This reduced the preparation time from several hours to less than two minutes. In addition, the minimal bacterial mass required for analysis was reduced from several milligrams to micrograms. The profiling of cellular fatty acids of Gram-positive and Gram-negative bacteria was achieved using three derivatization methods: preparation of methyl esters, β-picolinyl esters by Harvey’s method and a new method based on pyrolytic derivatization to β-picolinyl esters. It was shown that there are great similarities between profiles of bacterial fatty acids determined by the pyrolytic derivatization method and traditional preparation methods of picolinyl and methyl esters prior to GC analysis. Results obtained by application of the new technique have immense diagnostic value due to vast similarities between profiles of fatty acids derivatized to either picolinyl and methyl esters. Although the latter are referred to in the literature most often, mass spectra of picolinyl esters contain fragment ions that provide structural information about the chain branching, position of unsaturation, and other substituents.