Pittenauer Ernst, Allmaier Günter
Institute of Chemical Technologies and Analytics, Vienna University of Technology, Vienna, Austria.
J Am Soc Mass Spectrom. 2009 Jun;20(6):1037-47. doi: 10.1016/j.jasms.2009.01.009. Epub 2009 Feb 27.
Triacylglycerols were analyzed as cationized species (Li(+), Na(+), K(+)) by high-energy CID at 20 keV collisions utilizing MALDI-TOF/RTOF mass spectrometry. Precursor ions, based on M + Li-adduct ions exhibited incomplete fragmentation in the high and low m/z region whereas M + K-adducts did not show useful fragmentation. Only sodiated precursor ions yielded product ion spectra with structurally diagnostic product ions across the whole m/z range. The high m/z region of the CID spectra is dominated by abundant charge-remote fragmentation of the fatty acid substituents. In favorable cases also positions of double bonds or of hydroxy groups of the fatty acid alkyl chains could be determined. A-type product ions represent the end products of these charge-remote fragmentations. B- and C-type product ions yield the fatty acid composition of individual triacylglycerol species based on loss of either one neutral fatty acid or one sodium carboxylate residue, respectively. Product ions allowing fatty acid substituent positional determination were present in the low m/z range enabling identification of either the sn-1/sn-3 substituents (E-, F-, and G-type ions) or the sn-2 substituent (J-type ion). These findings were demonstrated with synthetic triacylglycerols and plant oils such as cocoa butter, olive oil, and castor bean oil. Typical features of 20 keV CID spectra of sodiated triacylglycerols obtained by MALDI-TOF/RTOF MS were an even distribution of product ions over the entire m/z range and a mass accuracy of +/-0.1 to 0.2 u. One limitation of the application of this technique is mainly the insufficient precursor ion gating after MS1 (gating window at 4 u) of species separated by 2 u.
利用基质辅助激光解吸电离飞行时间/反射飞行时间质谱（MALDI-TOF/RTOF MS），通过在20 keV碰撞能量下的高能碰撞诱导解离（CID），将三酰甘油分析为阳离子化物种（Li⁺、Na⁺、K⁺）。基于[M + Li]⁺加合物离子的前体离子在高和低m/z区域均表现出不完全碎片化，而[M + K]⁺加合物未显示出有用的碎片化。只有钠化前体离子在整个m/z范围内产生具有结构诊断性产物离子的产物离子谱。CID谱的高m/z区域主要由脂肪酸取代基的大量电荷远程碎片化主导。在有利的情况下，还可以确定脂肪酸烷基链中双键或羟基的位置。A型产物离子代表这些电荷远程碎片化的终产物。B型和C型产物离子分别基于损失一个中性脂肪酸或一个羧酸钠残基，得出各个三酰甘油物种的脂肪酸组成。允许确定脂肪酸取代基位置的产物离子存在于低m/z范围内，能够鉴定sn-1/sn-3取代基（E-、F-和G型离子）或sn-2取代基（J型离子）。这些发现通过合成三酰甘油和植物油（如可可脂、橄榄油和蓖麻油）得到了证实。通过MALDI-TOF/RTOF MS获得的钠化三酰甘油的20 keV CID谱的典型特征是产物离子在整个m/z范围内均匀分布，质量准确度为±0.1至0.2 u。该技术应用的一个局限性主要是在MS1（4 u的门控窗口）后对相差2 u分离的物种的前体离子门控不足。
