Department of Chemistry, Seoul National University, Seoul 151-742, Korea.
Anal Chem. 2012 Aug 21;84(16):7107-11. doi: 10.1021/ac3014077. Epub 2012 Jul 30.
Matrix-assisted laser desorption ionization of peptides was investigated using α-cyano-4-hydroxycinnamic acid as the matrix. In each experiment, a set of mass spectra was collected by repetitive irradiation of a spot on a sample. Even though shot-to-shot variation in spectral pattern was significant, it was reproducible for different spots and samples. Each spectrum was tagged with the temperature in the early plume (T(early)) estimated through kinetic analysis of the peptide ion survival probability. T(early) decreased as the shot continued because the thermal conduction got more efficient as the sample got thinner. From each spectral set collected under various experimental conditions, a spectrum tagged with a particular T(early) was selected. Then, patterns of the spectra thus selected were the same. The reaction quotient for the matrix-to-peptide proton transfer determined at a specified T(early) was independent of the sample composition, indicating quasi-thermal equilibrium for this reaction. Furthermore, the van't Hoff plots were linear, also indicating quasi-thermal equilibrium. This, together with the thermal kinetics for the fragmentation of peptide and matrix ions, is responsible for the reproducibility of the mass spectral pattern at a specified T(early).
采用α-氰基-4-羟基肉桂酸作为基质，研究了肽的基质辅助激光解吸电离。在每次实验中，通过对样品上的一个点进行重复辐照，收集一组质谱。尽管光谱模式的逐点变化非常显著，但对于不同的点和样品来说，它是可重复的。每个光谱都标有通过肽离子生存概率的动力学分析估计的早期羽流中的温度（T（早期））。由于随着样品变薄，热传导变得更加有效，因此 T（早期）随着射击的继续而降低。从在各种实验条件下收集的每个光谱集中，选择一个标记有特定 T（早期）的光谱。然后，选择的光谱的模式是相同的。在指定的 T（早期）下确定的基质-肽质子转移的反应商与样品组成无关，表明该反应处于准热平衡状态。此外，范特霍夫图是线性的，也表明准热平衡。这与肽和基质离子碎裂的热动力学一起，负责在指定的 T（早期）下质谱模式的重现性。
