Kolakowski Beata M, McCooeye Margaret A, Mester Zoltan
NRC, Institute for National Measurement Standards, Building M-12, 1200 Montreal Road, Ottawa, ON, Canada.
Rapid Commun Mass Spectrom. 2006;20(22):3319-29. doi: 10.1002/rcm.2739.
The separation and ion focusing properties of High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) depend on desolvated ions entering the device, leading to a compound-specific, reproducible compensation voltage (CV) for each ion. This study shows that the conditions identified for stable spray and satisfactory ion desolvation in normal electrospray ionization mass spectrometry (ESI-MS) operation might significantly differ from those required for FAIMS-MS. In a typical setup with high-flow electrospray conditions, ions could be incompletely desolvated, resulting in the formation of unidentified clusters with differing behavior in a FAIMS environment. This causes compound-specific shifts of as much as 10 V in CV values when the mobile phase composition and/or flow rate are varied. The shifts diminish and finally disappear when the flow rate of methanol, used as mobile phase, is reduced to 40 microL/min and that of acetonitrile to 20 microL/min. The reproducibility of the observed CV was determined by scanning the CV while infusing a five-component mixture into a 400 microL/min flow of methanol or 50:50 acetonitrile/water. The relative standard deviation (RSD) for these multiple scans ranged from 0.7% to 6%. Therefore, under a constant set of experimental parameters, the CV does not shift appreciably. These observations have an impact on method development strategies. High flow rates can be used with the FAIMS device, since the CV values are reproducible, but it is likely that clusters are forming. Therefore, CV scans should be performed under conditions which mimic the chromatographic elution or flow injection analysis conditions, including matrix composition, to minimize errors in CV determination. An alternative approach is to determine the liquid flow rate at which the CV becomes compound-specific and to split the mobile phase stream accordingly. These experimental results may be specific to the setup used for this study and may not be directly applicable to other instrument FAIMS devices.
高场不对称波形离子迁移谱（FAIMS）的分离和离子聚焦特性取决于进入该装置的去溶剂化离子，从而使得每种离子都有一个化合物特异性的、可重现的补偿电压（CV）。本研究表明，在常规电喷雾电离质谱（ESI-MS）操作中确定的稳定喷雾和令人满意的离子去溶剂化条件可能与FAIMS-MS所需的条件有显著差异。在典型的高流量电喷雾条件设置下，离子可能未完全去溶剂化，导致在FAIMS环境中形成行为各异的未识别簇。当流动相组成和/或流速变化时，这会导致CV值出现高达10 V的化合物特异性偏移。当用作流动相的甲醇流速降至40 μL/min且乙腈流速降至20 μL/min时，偏移减小并最终消失。通过在将五组分混合物注入400 μL/min的甲醇流或50:50乙腈/水流的同时扫描CV来确定观察到的CV的重现性。这些多次扫描的相对标准偏差（RSD）范围为0.7%至6%。因此，在一组恒定的实验参数下，CV不会有明显偏移。这些观察结果对方法开发策略有影响。由于CV值是可重现的，所以可以在FAIMS装置中使用高流速，但很可能会形成簇。因此，应在模拟色谱洗脱或流动注射分析条件（包括基质组成）的条件下进行CV扫描，以尽量减少CV测定中的误差。另一种方法是确定CV变得具有化合物特异性时的液体流速，并相应地分流流动相流。这些实验结果可能特定于本研究所使用的设置，可能无法直接应用于其他仪器的FAIMS装置。
