Duty cycle improvement for a quadrupole-time-of-flight mass spectrometer and its use for precursor ion scans
Duty cycle improvement for a quadrupole-time-of-flight mass spectrometer and its use for precursor ion scans
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DOI：
10.1255/ejms.377
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发表时间：
2000-01-01
影响因子：
1.3
通讯作者：
Chernushevich, IV
中科院分区：
文献类型：
--
作者：
Chernushevich, IV
通常，四极杆飞行时间（QqTOF）仪器受益于所有质量的同时记录，并且当记录全扫描时，其灵敏度高于三重四极杆。当仅必须监测单一类型的离子时，如在前体离子扫描或多反应监测（MRM）模式中，情况并非如此。这是因为TOF中的离子损失高于四极杆中的离子损失。这些损失的很大一部分是由于正交TOF仪器的低占空比，通常为5至30%。将离子捕获在碰撞室中，然后在与TOF提取同步的短脉冲串中将它们门控出来，可以以质量范围为代价恢复占空比。研究了不同条件下的离子俘获、门控和聚束机制。通过改变陷获和选通参数，可以实现不同的操作模式：从窄质量范围的100%占空比恢复到更宽质量范围的< 50%占空比。前一种模式最适合单碎片前体离子扫描，而当需要记录完整的产物离子光谱或执行多碎片前体离子扫描时，后者更好。前体离子扫描与肽和脂质获得的几个例子证明。灵敏度的提高范围从x15的亚铵碎片离子（m/z 86）到x5的同时记录的脂质片段与mit = 184和264。
Normally, quadrupole-time-of-flight (QqTOF) instruments benefit from a simultaneous recording of all masses, and their sensitivity is higher than that of a triple quadrupole when a full scan is recorded. This is not the case when only a single type of ion has to be monitored, as in precursor ion scanning or multiple-reaction monitoring (MRM) mode. This is because ion losses in TOF are higher than in a quadrupole, A significant part of these losses is due to the low duty cycle of an orthogonal TOF instrument, typically 5 to 30%, Trapping ions in the collision cell and then gating them out in short bursts synchronized with TOF extraction can restore the duty cycle at the expense of mass range. The mechanism of ion trapping, gating and bunching is studied under various conditions. By varying trapping and gating parameters, different modes of operation are achievable: from a 100% duty cycle restoration for a narrow mass range to < 50% duty cycle for a wider mass range. The former mode is best for a single-fragment precursor ion scan, whereas the latter is better when a full product-ion spectrum needs to be recorded, or when a multiple-fragment precursor ion scan is performed. Several examples of precursor ion scans obtained with peptides and lipids are demonstrated. Sensitivity improvements range from x15 for the immonium fragment ion (m/z 86) to x5 for simultaneous recording of lipid fragments with mit = 184 and 264.