Alvarez Jormarie, Cooks R Graham, Barlow S E, Gaspar Daniel J, Futrell Jean H, Laskin Julia
Department of Chemistry, Purdue Univeristy, West Lafayette, Indiana 47907, USA.
Anal Chem. 2005 Jun 1;77(11):3452-60. doi: 10.1021/ac0481349.
Mass-selected peptide ions produced by electrospray ionization were deposited onto fluorinated self-assembled monolayer surfaces (FSAM) surfaces by soft landing using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially designed for studying interactions of large ions with surfaces. Analysis of the modified surface was performed in situ by combining 2-keV Cs+ secondary ion mass spectrometry with FT-ICR detection of the sputtered ions (FT-ICR-SIMS). Regardless of the initial charge state of the precursor ion, the SIMS mass spectra included singly protonated peptide ion, peptide fragment ions, and peaks characteristic of the surface in all cases. In some experiments, multiply protonated peptide ions and [M + Au]+ ions were also observed upon SIMS analysis of modified surfaces. For comparison with the in situ analysis of the modified surfaces, ex situ analysis of some of the modified surfaces was performed by 25-keV Ga+ time-of-flight-secondary ion mass spectrometry (TOF-SIMS). The ex situ analysis demonstrated that a significant number of soft-landed peptide ions remain charged on the surface even when exposed to air for several hours after deposition. Charge retention of soft-landed ions dramatically increases the ion yields obtained during SIMS analysis and enables very sensitive detection of deposited material at less than 1% of monolayer coverage. Accumulation of charged species on the surface undergoes saturation due to coulomb repulsion between charges at close to 30% coverage. We estimated that close to 1 ng of peptide could be deposited on the spot area of 4 mm2 of the FSAM surface without reaching saturation.
通过电喷雾电离产生的质量选择肽离子，使用专门设计用于研究大离子与表面相互作用的傅里叶变换离子回旋共振质谱仪（FT-ICR MS），通过软着陆沉积在氟化自组装单分子层表面（FSAM）上。通过将2 keV Cs⁺二次离子质谱与溅射离子的FT-ICR检测（FT-ICR-SIMS）相结合，对改性表面进行原位分析。无论前体离子的初始电荷状态如何，在所有情况下，SIMS质谱都包括单质子化肽离子、肽片段离子以及表面特征峰。在一些实验中，对改性表面进行SIMS分析时还观察到了多质子化肽离子和[M + Au]⁺离子。为了与改性表面的原位分析进行比较，通过25 keV Ga⁺飞行时间二次离子质谱（TOF-SIMS）对一些改性表面进行了非原位分析。非原位分析表明，即使在沉积后暴露于空气中数小时，大量软着陆的肽离子仍保持表面带电。软着陆离子的电荷保留显著提高了SIMS分析期间获得的离子产率，并能够在单层覆盖率小于1%的情况下非常灵敏地检测沉积材料。由于电荷之间的库仑排斥，表面带电物种的积累在接近30%覆盖率时会达到饱和。我们估计，在不达到饱和的情况下，接近1 ng的肽可以沉积在FSAM表面4 mm²的斑点区域上。
