Jansen Robert, Lachatre Gérard, Marquet Pierre
Department of Pharmacology-Toxicology, University Hospital, 2 av. Martin-Luther-King, 87042 Limoges cedex, France.
Clin Biochem. 2005 Apr;38(4):362-72. doi: 10.1016/j.clinbiochem.2004.11.003.
To compare the mass spectra obtained using a linear-ion-trap (LIT) tandem mass spectrometer (QTRAP) operated in the "enhanced product ion scan" (EPI) mode with those obtained in the classical triple-quadrupole product ion scan (PIS) mode run on the same as well as on two other instruments (TSQ-Quantum and Quattro-Micro).
After tentative standardization of ion fragmentation and transmission in both polarities using a reference compound (glafenine) on the three instruments, eight test compounds detected in the positive mode and five in the negative mode were systematically infused in different ionization sources and spectral acquisition performed over approximately 5 s. The relative intensity of the ions present in the resulting spectra was quantitatively and statistically compared. Also, the intra-day and inter-day variabilities of these relative intensities, as well as the effect of increasing compound concentration, were studied using QTRAP operated in EPI mode.
The EPI and PIS modes operated on a single LIT MS/MS instrument resulted in significant differences in relative ion intensities in both polarities, and so did the other two instruments despite prior standardization with glafenine. Some fragments could be absent in certain spectra, but no unexpected or unique fragments showed up. Intra-day variability was smaller in the LIT EPI than in the regular PIS mode and in the positive than in the negative polarity. In EPI mode, both intra- and inter-day variabilities increased when the relative intensity decreased. The effect of increasing concentration on the relative intensity of major and minor ions was small but significant in both polarities. Finally, contamination and cleansing of the ionization source also had noticeable effects on MS/MS spectra, though the cause is unclear.
MS/MS spectra do not offer the expected inter-instrument reproducibility despite an attempt at standardizing the fragmentation conditions using a reference compound. However, although the inter-instrument differences in ion relative intensity were significant, the spectra obtained looked almost similar. This suggests that in library searching algorithms, higher weight should be assigned for the m/z ratios than for their relative intensity in the spectra.
比较使用线性离子阱（LIT）串联质谱仪（QTRAP）在“增强产物离子扫描”（EPI）模式下获得的质谱图与在经典三重四极杆产物离子扫描（PIS）模式下在同一台以及另外两台仪器（TSQ-Quantum和Quattro-Micro）上获得的质谱图。
在三台仪器上使用参考化合物（格拉非宁）对两种极性下的离子碎裂和传输进行初步标准化后，系统地将在正模式下检测到的八种测试化合物和在负模式下检测到的五种测试化合物注入不同的电离源，并在大约5秒内进行光谱采集。对所得光谱中存在的离子的相对强度进行定量和统计比较。此外，使用在EPI模式下运行的QTRAP研究了这些相对强度的日内和日间变异性，以及化合物浓度增加的影响。
在单台LIT MS/MS仪器上运行的EPI和PIS模式在两种极性下的相对离子强度均存在显著差异，另外两台仪器尽管事先用格拉非宁进行了标准化处理，但也存在这种情况。某些光谱中可能缺少一些碎片，但没有出现意外或独特的碎片。LIT EPI模式下的日内变异性比常规PIS模式下小，且正模式下比负模式下小。在EPI模式下，当日内和日间变异性的相对强度降低时，两者都会增加。浓度增加对主要和次要离子相对强度的影响虽小但在两种极性下均显著。最后，电离源的污染和清洁对MS/MS光谱也有明显影响，但其原因尚不清楚。
尽管尝试使用参考化合物对碎裂条件进行标准化，但MS/MS光谱并未提供预期的仪器间重现性。然而，尽管离子相对强度的仪器间差异显著，但获得的光谱看起来几乎相似。这表明在库搜索算法中，对于光谱中的m/z比值应比其相对强度赋予更高的权重。
