Division of BioAnalytical Chemistry, Amsterdam Institute for Molecules, Medicines and Systems, Department of Chemistry and Pharmaceutical Sciences , Vrije Universiteit Amsterdam , de Boelelaan 1085 , 1081 HV Amsterdam , The Netherlands.
Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Faculty of Sciences , University of Alcalá , Carretera Madrid-Barcelona Km. 33600 , 28871 , Alcalá de Henares , Madrid , Spain.
Anal Chem. 2019 Mar 5;91(5):3277-3285. doi: 10.1021/acs.analchem.8b03661. Epub 2019 Feb 12.
A novel analytical method based on hybrid trapped ion mobility spectrometry-time-of-flight mass spectrometry (TIMS-TOFMS) has been developed to achieve fast enantiomeric separation of amino acids (AAs). Resolution of chiral AAs was achieved by forming diastereomers through derivatization with the chiral agent (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC), avoiding the use of reference compounds. Electrospray ionization (ESI) in positive mode yielded sodiated FLEC-AAs ions of which the diastereomers could be separated by TIMS. The effect of other alkali metal ions (such as Li and K) on the enantioselectivity was studied, but chiral discrimination was only observed for Na. TIMS conditions, including voltage ramp, ramp time, and accumulation time were optimized for each AA, and collision cross sections (CCSs) were determined for all diastereomers. The migration order of the DL enantiomers was found to be dependent on the structure of the AA. The resulting TIMS resolution (K0/ΔK0) for the FLEC-AA diastereomers on average was 115, requiring a mobility (K0) difference of about 0.009 cm/(V s) to achieve 50%-valley separation. From the 21 AAs studied, enantiomer separation was achieved for 17 AAs with mobility differences ranging from 0.009 for lysine up to 0.061 cm/(V s) for asparagine. Moreover, the presented methodology provided mutual separation of various AAs, allowing chiral analysis of multiple AAs simultaneously which may be challenging with previous enantioselective IMS approaches. It appeared possible to fully resolve all studied DL-AAs using three distinct TIMS methods, resulting in a total MS run time of about 3 min (1 min per method) and a total analysis time (including derivatization) of less than 15 min. The method demonstrated capable to determine enantiomeric ratios down to 2.5% with detection limits for the D enantiomers in the nanomolar range. This new TIMS-based methodology opens up possibilities for easy and fast analysis of AA enantiomers.
一种基于混合离子淌度谱-飞行时间质谱（TIMS-TOFMS）的新型分析方法已经被开发出来，以实现氨基酸（AA）的快速对映体分离。通过与手性试剂（+）-1-（9-芴基）乙基氯甲酸酯（FLEC）衍生化形成非对映异构体，从而实现手性 AA 的分辨率，避免使用参考化合物。正离子模式下的电喷雾电离（ESI）产生 FLEC-AA 加钠离子，其中非对映异构体可以通过 TIMS 分离。研究了其他碱金属离子（如 Li 和 K）对对映选择性的影响，但仅观察到 Na 具有手性歧视。优化了每种 AA 的 TIMS 条件，包括电压斜坡、斜坡时间和积累时间，并确定了所有非对映异构体的碰撞截面（CCS）。发现 DL 对映体的迁移顺序取决于 AA 的结构。FLEC-AA 非对映异构体的平均 TIMS 分辨率（K0/ΔK0）为 115，需要大约 0.009 cm/（V s）的迁移率（K0）差异才能实现 50%-谷分离。在所研究的 21 种 AA 中，17 种 AA 实现了对映体分离，其迁移率差异从赖氨酸的 0.009 到天冬酰胺的 0.061 cm/（V s）不等。此外，所提出的方法提供了各种 AA 的相互分离，允许同时分析多种 AA，这可能是以前的对映选择性 IMS 方法所具有挑战性的。似乎可以使用三种不同的 TIMS 方法完全分离所有研究的 DL-AA，从而使总 MS 运行时间约为 3 分钟（每种方法 1 分钟），总分析时间（包括衍生化）不到 15 分钟。该方法能够以 2.5%的对映体比例进行测定，检测到的 D 对映体的检测限在纳摩尔范围内。这种新的基于 TIMS 的方法为 AA 对映体的简单快速分析开辟了可能性。
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