Department of Pharmaceutical Technology Program, Chulalongkorn University, Bangkok 10330, Thailand.
Rapid Commun Mass Spectrom. 2010 Sep 15;24(17):2547-53. doi: 10.1002/rcm.4673.
Isobaric product ions cannot be differentiated by exact mass determinations, although in some cases deuterium labeling can provide useful structural information for identifying isobaric ions. Proposed fragmentation pathways of fentanyl were investigated by electrospray ionization ion trap mass spectrometry coupled with deuterium labeling experiments and spectra of regiospecific deuterium labeled analogs. The major product ion of fentanyl under tandem mass spectrometry (MS/MS) conditions (m/z 188) was accounted for by a neutral loss of N-phenylpropanamide. 1-(2-Phenylethyl)-1,2,3,6-tetrahydropyridine (1) was proposed as the structure of the product ion. However, further fragmentation (MS(3)) of the fentanyl m/z 188 ion gave product ions that were different from the product ion in the MS/MS fragmentation of synthesized 1, suggesting that the m/z 188 product ion from fentanyl includes an isobaric structure different from the structure of 1. MS/MS fragmentation of fentanyl in deuterium oxide moved one of the isobars to 1 Da higher mass, and left the other isobar unchanged in mass. Multistage mass spectral data from deuterium-labeled proposed isobaric structures provided support for two fragmentation pathways. The results illustrate the utility of multistage mass spectrometry and deuterium labeling in structural assignment of isobaric product ions.
等质量离子不能通过精确质量测定来区分，尽管在某些情况下氘标记可以为识别等质量离子提供有用的结构信息。通过电喷雾电离离子阱质谱联用氘标记实验和区域特异性氘标记类似物的光谱研究了芬太尼的拟议断裂途径。在串联质谱（MS/MS）条件下（m/z 188），芬太尼的主要产物离子归因于 N-苯丙酰胺的中性丢失。提出 1-（2-苯乙基）-1,2,3,6-四氢吡啶（1）作为产物离子的结构。然而，进一步对芬太尼 m/z 188 离子进行 MS(3)碎裂，得到的产物离子与合成的 1 的 MS/MS 碎裂产物离子不同，这表明来自芬太尼的 m/z 188 产物离子包含与 1 的结构不同的等质量结构。氘氧化合物中芬太尼的 MS/MS 碎裂将一个等质量体移动到 1 Da 更高的质量，而另一个等质量体的质量不变。来自氘标记拟议等质量结构的多级质谱数据为两种断裂途径提供了支持。结果表明多阶段质谱和氘标记在等质量产物离子结构鉴定中的应用。
