Optimization of the mass spectrometric analysis of triacylglycerols using negative-ion chemical ionization with ammonia |
| |
Authors: | Päivi Laakso Heikki Kallio |
| |
Affiliation: | (1) Department of Biochemistry and Food Chemistry, University of Turku, FIN-20500 Turku, Finland |
| |
Abstract: | Conditions for the mass spectrometric analysis of triacylglycerols,via direct exposure probe, with ammonia negative-ion chemical ionization were optimized. Triacylglycerols were most favorably
ionized, using the reactant gas pressure of approximately 8500 mtorr at the ion source temperature of 200°C with the instrumentation
used. Abundant M-H]− ions were produced under these conditions without the formation of M+35]− cluster ions, which would interfere with the molecular weight region of triacylglycerols in the spectra. A rapid desorption
of the sample from the probe wire is recommended, using a relatively high heating rate (approximately 40 mA s−1), to minimize thermal degradation of unsaturated molecules and the reducing effect of double bonds on the mass spectrometric
response of triacylglycerols. Furthermore, the abundance of M-H]− ion was enhanced by rapid heating, which we found to be important to improve the sensitivity. The appropriate amount of sample
applied to the rhenium wire was in the region of 50–300 ng for one determination, i.e., only a few nanograms of a single triacylglycerol
is required for production of a reliable spectrum. The reproducibility of the method was good as demonstrated with standards
and a raspberry seed oil sample. The described mass spectrometric method is a fast and potentially useful tool for semiquantitative
determination of triacylglycerol mixtures of various fats and oils. The discrimination, caused by differences in molecular
size and unsaturation of triacylglycerols with 50 to 56 acyl carbons, was negligible under our optimized ionization conditions,
thus, no correction factors were needed. These findings have not yet been verified with instruments in other laboratories.
However, the present study shows how the analysis of triacylglycerols can be improved, regardless of the instrument, by optimization
of the analytical conditions. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|