Institut de Chimie et Procédés pour l'Énergie, l'Environnement et la Santé (ICPEES) - Physico-Chimie de l'Atmosphère, Université de Strasbourg, Strasbourg, France.
Laboratoire de Spectrométrie de Masse des Interactions et des Systèmes (LSMIS), Université de Strasbourg, Strasbourg, France.
Rapid Commun Mass Spectrom. 2022 Jul 15;36(13):e9307. doi: 10.1002/rcm.9307.
Multiple Reaction Monitoring (MRM) is a sensitive and selective detection mode for target trace-level analysis. However, it requires the fragmentation of labile bonds which are not present in molecules such as Polycyclic Aromatic Hydrocarbons (PAHs) and their heterocyclic derivatives (PANHs, PASHs).
We present the application of an alternative tandem mass spectrometry (MS/MS) mode called "pseudo-MRM" for the GCMS/MS analysis of Polycyclic Aromatic Compounds (PACs). This mode is based on the monitoring of transitions with no mass loss between the precursor and the product ion. Pseudo-MRM peak areas were compared with those of classic MRM on three different mass spectrometers: two triple quadrupoles and an ion trap.
For all non-polar PACs studied here (PAHs, PANHs and PASHs), the pseudo-MRM transition was always the most intense. The classic MRM transitions exhibited peak areas 2 to 5 times lower. On the contrary, for the functionalized PACs (oxygenated and nitrated PAHs), classic MRM was favored over pseudo-MRM. These observations were confirmed on two triple quadrupoles (QqQs), and the real-world applicability of pseudo-MRM on QqQs was validated by the successful analysis of Diesel PM. However, a comparison with an ion trap showed that pseudo-MRM was never favored on that instrument, which caused fragmentation of non-polar PACs in MS/MS.
The results of this study show an important gain in sensitivity when using pseudo-MRM instead of MRM for non-polar PACs on QqQ instruments. The selectivity of MRM is preserved in pseudo-MRM by applying non-zero collision energies to which only these non-polar PACs are resistant, not the isobaric interferences. No interference issue was observed when analyzing Diesel PM, a complex matrix, with our pseudo-MRM method. Therefore, we advise for a broader use of this MS/MS mode for trace-level determination of non-polar PAHs.
多反应监测（MRM）是一种用于痕量分析的灵敏且选择性的检测模式。然而，它需要断裂不稳定的键，而这些键在多环芳烃（PAHs）及其杂环衍生物（PANHs、PASHs）等分子中并不存在。
我们提出了一种替代的串联质谱（MS/MS）模式，称为“伪-MRM”，用于气相色谱-质谱联用（GC-MS/MS）分析多环芳烃（PACs）。这种模式基于监测在母离子和产物离子之间没有质量损失的跃迁。在三台不同的质谱仪上（两台三重四极杆和一台离子阱），比较了伪-MRM 峰面积与经典 MRM 的峰面积。
对于我们研究的所有非极性 PACs（PAHs、PANHs 和 PASHs），伪-MRM 跃迁始终是最强的。经典 MRM 跃迁的峰面积低 2 到 5 倍。相反，对于功能化的 PACs（含氧和含氮的 PAHs），经典 MRM 比伪-MRM 更有利。在两台三重四极杆（QqQs）上得到了这些观察结果的证实，并且通过对柴油机颗粒物的成功分析验证了伪-MRM 在 QqQs 上的实际应用。然而，与离子阱的比较表明，在该仪器上，伪-MRM 从未受到青睐，这导致非极性 PACs 在 MS/MS 中发生了断裂。
本研究的结果表明，在 QqQ 仪器上，使用伪-MRM 替代经典 MRM 对非极性 PACs 进行分析时，灵敏度有显著提高。通过对只有这些非极性 PACs 能抵抗的非零碰撞能量的应用，在伪-MRM 中保留了 MRM 的选择性，而不是同量异位素干扰。在用我们的伪-MRM 方法分析复杂基质柴油机颗粒物时，未观察到干扰问题。因此，我们建议更广泛地使用这种 MS/MS 模式来痕量测定非极性 PAHs。
