Routine gas chromatographic/mass spectrometric analysis of fatty acid methyl esters using the ion trap detector.

About 60 long-chain fatty acids occur naturally in lipids of biological tissues and fluids, oils, fats and waxes. The ion trap detector (ITD) offers a convenient but powerful means for the routine analysis by gas chromatography/mass spectrometry of such fatty acids as their methyl esters (FAMES). Enhanced [M + 1]+ ions may be formed at higher sample levels of 50 ng or more. However, spectra still retain a predominantly electron impact (EI) character. Using the classical mass spectral performance test compound methyl stearate as an example, good library comparisons were obtained for spectra run over a dynamic range of 2 pg to 225 ng, when a mid-range ITD spectrum run on 7.5 ng was used as a reference. Almost equally good spectral comparisons were found with literature reference spectra run on both quadrupole and sector conventional mass spectrometers. Using human plasma phospholipid FAMES as an example, along with an ITD-generated EI spectral library of FAMES standards, it was seen that for most of the components present the mass spectral library comparison was good enough to permit identification based on mass spectrometry alone. For all components, a combination of gas chromatographic retention index and mass spectral information permitted an unequivocal identification.

The alleged antithiamine activity of o-diphenols: an artefact of oxygen in the thiochrome method?

1H-n. m. r. and t. l. c. measurements show that ortho-diphenols induced little or no chemical change in thiamine when co-dissolved in aqueous solution at pH 7.8. Thiamine determinations on the same solutions by the classical thiochrome method are critically susceptible to the amount of dissolved oxygen. An oxygen saturated equimolar solution of thiamine and pyrocatechol (0.03 mM), after 24 hours at pH 7.8 and at 37 degree, gives almost no thiochrome fluorescence response unless the solution is first degassed to remove all traces of oxygen. It is suggested that earlier literature reports of the pronounced anti thiamine effect of o-diphenols were erroneously based on this apparent disappearance of thiamine when oxygen is not excluded.

Evidence against the reported antithiamine effect of caffeic and chlorogenic acids.

Contrary to earlier literature reports, chlorogenic acid (I) is shown to have little or no deleterious effect on thiamine (II) when the 2 compounds are codissolved in aqueous solution. Evidence from nmr spectroscopy and from t. l. c. determination demonstrate that when II is heated at 60 degrees C and at pH 7.8 for 24h, about 10% is destroyed. This result is the same whether I is present or not. Incubating II with I or with caffeic acid (III) in a phosphate buffer at pH 7 or in thiamine assay medium at pH 6 for up to 24h at 37 degrees C did not reduce the growth activity of II or Lactobacillus viridescens. We conclude that I and III are not antithiamine agents.