Department of Chemistry, The Chinese University of Hong Kong, Kowloon 999077, Hong Kong SAR, P. R. China.
Shandong Analysis and Test Centre, School of Pharmaceutical Sciences, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250316, Shandong, PR China.
Anal Chem. 2023 Jun 13;95(23):9060-9067. doi: 10.1021/acs.analchem.3c01411. Epub 2023 May 25.
Reproducible peptide oxidation was observed using a homebuilt liquid microjunction-surface sampling probe (LMJ-SSP) platform for analyzing peptide standards. Although electrochemical oxidation and corona discharges have previously been associated with analyte oxidation in electrospray ionization (ESI) and ESI-related ambient ionization mass spectrometry (MS) methods, they were unlikely the causes for the peptide oxidation observed in the LMJ-SSP studies. A systematic investigation demonstrated that analyte oxidation was induced during the droplet drying on a solid surface through liquid-solid electrification processes. To minimize unwanted analyte oxidation, the water content in the sample solution should be decreased and the use of hydroxyl-functionalized substrates, such as glass slides, should be avoided. In addition, if water is an essential solvent component, adding an antioxidant, such as ascorbic acid, to the sample solution before droplet evaporation on the solid surface could lower the percentage of analyte oxidation. The present findings apply to all the MS methods that involve drying microliters of sample solution onto a suitable substrate in their sample preparation protocols.
使用自制的液相微萃取-表面采样探针（LMJ-SSP）平台分析肽标准品时，观察到可重现的肽氧化。虽然电化学氧化和电晕放电以前与电喷雾电离（ESI）和 ESI 相关的环境电离质谱（MS）方法中的分析物氧化有关，但它们不太可能是 LMJ-SSP 研究中观察到的肽氧化的原因。系统研究表明，在固体表面上通过液-固静电过程，在液滴干燥过程中诱导了分析物氧化。为了最大限度地减少不必要的分析物氧化，应降低样品溶液中的含水量，并避免使用羟基功能化的基底，如载玻片。此外，如果水是必需的溶剂成分，则在液滴在固体表面上蒸发之前，向样品溶液中添加抗坏血酸等抗氧化剂，可降低分析物氧化的百分比。本研究结果适用于所有涉及在其样品制备方案中将微升样品溶液干燥到合适基底上的 MS 方法。
