Internal Energy of Ions Generated by Matrix-Assisted Laser Desorption/Ionization
详细信息 查看全文
- 作者：Guanghong Luo ; Ioan Marginean ; and Akos Vertes
- 刊名：Analytical Chemistry
- 出版年：2002
- 出版时间：December 15, 2002
- 年：2002
- 卷：74
- 期：24
- 页码：6185 - 6190
- 全文大小：103K
- 年卷期：v.74,no.24(December 15, 2002)
- ISSN：1520-6882
文摘
To provide an objective measure of the correlation between the internal energy content of ions generated bymatrix-assisted laser desorption/ionization (MALDI) andthe matrix properties, a series of well-characterizedbenzyl-substituted benzylpyridinium salts were used asthermometer molecules (TMs). To determine the internalenergy variations of analyte ions, the survival yields of TMmolecular ions were measured in three different matrixes,
-cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SA), and 2,5-dihydroxybenzoic acid (DHB). Statistical analysis of extensive survival yield data indicated that there werediscernible differences among the studied matrixes. Theexperimental survival yields of the TM ions were used tocalculate the unimolecular decomposition rate coefficient.Corresponding theoretical reaction rate coefficients werecalculated based on the Rice-Ramsperger-Kassel-Marcus (RRKM) theory for different internal energies ofthe TMs. The internal energies of the ions were obtainedby projecting the experimental rate coefficient values ontothe theoretical curves obtained by the RRKM calculations.Molecular ions of the analytes showed decreasing survivalyields and consequently increasing internal energies inthe three matrixes in the following order: CHCA, SA, andDHB with "cold", "intermediate", and "hot" characteristics, respectively. Qualitatively, this could be interpretedas a significant departure from earlier observations suggesting an opposite trend. The classification as hot andcold matrixes should be further qualified by accountingfor the influence of laser pulse energy and the nature ofthe analyte. Higher laser pulse energy led to an elevatedlevel of energy transferred to the analyte, which in turnresulted in a diminished survival yield of the analytemolecular ion. It is quite possible that the assignment ofhot and cold reverses as the analyte or the laser energychanges. These findings can help predict the outcome ofpostsource decay experiments and clarify the concept ofhot and cold matrixes in MALDI mass spectrometry.
-cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SA), and 2,5-dihydroxybenzoic acid (DHB). Statistical analysis of extensive survival yield data indicated that there werediscernible differences among the studied matrixes. Theexperimental survival yields of the TM ions were used tocalculate the unimolecular decomposition rate coefficient.Corresponding theoretical reaction rate coefficients werecalculated based on the Rice-Ramsperger-Kassel-Marcus (RRKM) theory for different internal energies ofthe TMs. The internal energies of the ions were obtainedby projecting the experimental rate coefficient values ontothe theoretical curves obtained by the RRKM calculations.Molecular ions of the analytes showed decreasing survivalyields and consequently increasing internal energies inthe three matrixes in the following order: CHCA, SA, andDHB with "cold", "intermediate", and "hot" characteristics, respectively. Qualitatively, this could be interpretedas a significant departure from earlier observations suggesting an opposite trend. The classification as hot andcold matrixes should be further qualified by accountingfor the influence of laser pulse energy and the nature ofthe analyte. Higher laser pulse energy led to an elevatedlevel of energy transferred to the analyte, which in turnresulted in a diminished survival yield of the analytemolecular ion. It is quite possible that the assignment ofhot and cold reverses as the analyte or the laser energychanges. These findings can help predict the outcome ofpostsource decay experiments and clarify the concept ofhot and cold matrixes in MALDI mass spectrometry.