Laakso P, Kallio H
Department of Biochemistry and Food Chemistry, University of Turku, Finland.
Lipids. 1996 Jan;31(1):33-42. doi: 10.1007/BF02522407.
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 degrees 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.
通过直接进样探头，采用氨负离子化学电离对三酰甘油进行质谱分析的条件得到了优化。在所使用的仪器条件下，当离子源温度为200℃、反应气压力约为8500毫托时，三酰甘油最有利于电离。在这些条件下会产生大量的[M-H]-离子，且不会形成会干扰光谱中三酰甘油分子量区域的[M + 35]-簇离子。建议使用相对较高的加热速率（约40 mA s-1）使样品从探头丝上快速解吸，以尽量减少不饱和分子的热降解以及双键对三酰甘油质谱响应的还原作用。此外，快速加热可增强[M-H]-离子的丰度，我们发现这对提高灵敏度很重要。用于铼丝的合适样品量为一次测定50-300 ng，即产生可靠光谱仅需几纳克单一三酰甘油。用标准品和树莓籽油样品证明该方法的重现性良好。所描述的质谱方法是一种快速且潜在有用的工具，可用于各种油脂三酰甘油混合物的半定量测定。在我们优化的电离条件下，由具有50至56个酰基碳的三酰甘油分子大小和不饱和度差异引起的歧视可忽略不计，因此无需校正因子。这些发现尚未在其他实验室的仪器上得到验证。然而，本研究表明，无论使用何种仪器，通过优化分析条件都可以改进三酰甘油的分析。
