Gong Xiaoxia, Zhang Dong, Embile Inah B, She Yue, Shi Songyue, Gamez Gerardo
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States.
J Am Soc Mass Spectrom. 2020 Sep 2;31(9):1981-1993. doi: 10.1021/jasms.0c00246. Epub 2020 Aug 18.
Thin-layer chromatography (TLC) is a widespread technique because it allows fast, simple, and inexpensive analyte separations. In addition, direct analysis of the compounds separated on TLC plates via mass spectrometry (MS) has been shown to provide high sensitivity and selectivity while avoiding time-consuming sample extraction protocols. Here, direct desorption low-temperature plasma-mass spectrometry (LTP-MS) as well as diode laser assisted desorption (LD) LTP-MS are studied for direct spatially resolved analysis of compounds from TLC plates. Qualitative and quantitative characterization of amino acids, pharmaceuticals, and structural isomers were performed. The nature of the TLC plate stationary phase was found to have a significant influence, together with the analyte's characteristics, on the desorption efficiency. Tandem MS is shown to greatly improve the limits of detection (LODs). Direct desorption LTP-MS, without external thermal assisted desorption, demonstrates its best performance with cellulose TLC plates (LODs, 0.01 ng/mm to 2.55 ng/mm) and restricted performance with normal-phase (NP) TLC plates (several analytes without observable signal). LD LTP-MS, with systematic optimization of irradiance and focal point diameter, is shown to overcome the direct-desorption limitations and reach significantly improved LODs with NP TLC plates (up to ×1000 better). In addition, a wide-ranging characterization of amino acid analytical figures of merit with LD LTP-MS shows that LODs from 84 pg/mm down to 0.3 pg/mm are achieved on NP TLC plates.
薄层色谱法（TLC）是一种广泛应用的技术，因为它能够实现快速、简单且成本低廉的分析物分离。此外，通过质谱（MS）对TLC板上分离的化合物进行直接分析已被证明具有高灵敏度和选择性，同时避免了耗时的样品提取流程。在此，研究了直接解吸低温等离子体质谱法（LTP-MS）以及二极管激光辅助解吸（LD）LTP-MS用于对TLC板上的化合物进行直接空间分辨分析。对氨基酸、药物和结构异构体进行了定性和定量表征。发现TLC板固定相的性质与分析物的特性一起对解吸效率有显著影响。串联质谱显示极大地提高了检测限（LOD）。无外部热辅助解吸的直接解吸LTP-MS在纤维素TLC板上表现出最佳性能（LOD为0.01 ng/mm至2.55 ng/mm），而在正相（NP）TLC板上性能受限（几种分析物无可观察信号）。通过对辐照度和焦点直径进行系统优化的LD LTP-MS显示能够克服直接解吸的局限性，并在NP TLC板上实现显著改善的LOD（提高多达1000倍）。此外，使用LD LTP-MS对氨基酸分析性能指标进行的广泛表征表明，在NP TLC板上实现了从84 pg/mm至0.3 pg/mm的LOD。
