Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu, 300, Taiwan.
Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300, Taiwan.
Anal Bioanal Chem. 2022 Jul;414(16):4633-4643. doi: 10.1007/s00216-022-04080-w. Epub 2022 Apr 20.
A sharp metal needle used as the ionization emitter in conventional atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) is usually required for analyte ionization through corona discharge (i.e., gas discharge). Nevertheless, we herein demonstrate that an insulating fiber (tip diameter: 10-60 µm; length: ~ 1 cm) made of glass or bamboo can function as an APCI-like ionization emitter. Although no direct electric contact is made on the fiber, the ionization of volatiles and semi-volatiles occurs when the fiber is placed close (~ 1 mm) to the inlet of the mass spectrometer. No analyte ion signals can be observed without placing the insulating fiber in front of the mass spectrometer. The generation of ion species mainly relies on the electric field provided by the mass spectrometer. Presumably, owing to the high electric field provided by the mass spectrometer, the dielectric breakdown voltages of gas molecules in the air and the fiber are overcome, leading to the ionization of analytes in gas phase. In addition, the insulating fiber can function as a holder for sample solutions. Electrospray ionization-like processes derived from polar analytes such as amino acids, peptides, and proteins can readily occur when the insulating fiber deposited with a sample droplet is placed close to the inlet of the mass spectrometer. The feasibility of using the current approach for the detection of nonpolar and polar analytes from complex fetal bovine serum samples without tedious sample pretreatment is demonstrated in this work. The main advantage of using the suggested fiber is that the fiber can be used as the sampling probe to pick up samples and placed in front of a mass spectrometer for direct MS analysis. The application of using a robust, insulating, and disposable probe to pick up samples from real samples such as onion, honey, and pork samples followed by direct MS analysis is also demonstrated.
常规大气压化学电离（APCI）质谱（MS）中使用的尖锐金属针通常用于通过电晕放电（即气体放电）使分析物电离。然而，我们在此证明，由玻璃或竹子制成的绝缘纤维（尖端直径：10-60 µm；长度：1 cm）可以用作 APCI 样电离发射器。尽管纤维上没有直接的电接触，但当纤维靠近（1 mm）质谱仪入口时，挥发性和半挥发性物质的电离就会发生。如果不在质谱仪前放置绝缘纤维，则无法观察到分析物离子信号。离子种类的产生主要依赖于质谱仪提供的电场。据推测，由于质谱仪提供的电场很高，空气中的气体分子和纤维的介电击穿电压被克服，导致气相中分析物的电离。此外，绝缘纤维可以作为样品溶液的支架。当沉积有样品液滴的绝缘纤维靠近质谱仪入口时，类似于电喷雾电离的过程很容易从极性分析物（如氨基酸、肽和蛋白质）中发生。本工作证明了无需繁琐的样品预处理即可使用当前方法从复杂的胎牛血清样品中检测非极性和极性分析物的可行性。使用建议的纤维的主要优点是纤维可以用作采样探针来采集样品，并将其放置在质谱仪前进行直接 MS 分析。还展示了使用坚固、绝缘且一次性的探针从洋葱、蜂蜜和猪肉等实际样品中采集样品并直接进行 MS 分析的应用。
