Moskovets Eugene, Misharin Alexander, Laiko Viktor, Doroshenko Vladimir
MassTech Inc., 6992 Columbia Gateway Dr., Columbia, MD 21046, USA.
MassTech Inc., 6992 Columbia Gateway Dr., Columbia, MD 21046, USA.
Methods. 2016 Jul 15;104:21-32. doi: 10.1016/j.ymeth.2016.02.009. Epub 2016 Feb 17.
A comparative MS study was conducted on the analytical performance of two matrix-assisted laser desorption/ionization (MALDI) sources that operated at either low pressure (∼1Torr) or at atmospheric pressure. In both cases, the MALDI sources were attached to a linear ion trap mass spectrometer equipped with a two-stage ion funnel. The obtained results indicate that the limits of detection, in the analysis of identical peptide samples, were much lower with the source that was operated slightly below the 1-Torr pressure. In the low-pressure (LP) MALDI source, ion signals were observed at a laser fluence that was considerably lower than the one determining the appearance of ion signals in the atmospheric pressure (AP) MALDI source. When the near-threshold laser fluences were used to record MALDI MS spectra at 1-Torr and 750-Torr pressures, the level of chemical noise at the 1-Torr pressure was much lower compared to that at AP. The dependency of the analyte ion signals on the accelerating field which dragged the ions from the MALDI plate to the MS analyzer are presented for the LP and AP MALDI sources. The study indicates that the laser fluence, background gas pressure, and field accelerating the ions away from a MALDI plate were the main parameters which determined the ion yield, signal-to-noise (S/N) ratios, the fragmentation of the analyte ions, and adduct formation in the LP and AP MALDI MS methods. The presented results can be helpful for a deeper insight into the mechanisms responsible for the ion formation in MALDI.
对两种基质辅助激光解吸/电离（MALDI）源的分析性能进行了比较质谱研究，这两种源分别在低压（约1托）或大气压下运行。在这两种情况下，MALDI源都连接到配备了两级离子漏斗的线性离子阱质谱仪上。获得的结果表明，在分析相同的肽样品时，在略低于1托压力下运行的源的检测限要低得多。在低压（LP）MALDI源中，在激光能量密度远低于在大气压（AP）MALDI源中确定离子信号出现的能量密度时就观察到了离子信号。当使用接近阈值的激光能量密度在1托和750托压力下记录MALDI质谱图时，1托压力下的化学噪声水平比大气压下的要低得多。给出了低压和大气压MALDI源中分析物离子信号对将离子从MALDI板拖到质谱分析仪的加速场的依赖性。该研究表明，激光能量密度、背景气体压力以及将离子从MALDI板加速离开的场是决定低压和大气压MALDI质谱方法中离子产率、信噪比（S/N）、分析物离子碎片化和加合物形成的主要参数。所呈现的结果有助于更深入地了解MALDI中离子形成的机制。
