Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization

Lu, I‐Chung; Lee, Chuping; Lee, Yuan-Tseh; Ni, Chi-Kung

doi:10.1146/annurev-anchem-071114-040315

Cited by 60 publications

(60 citation statements)

References 59 publications

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“…Studies have demonstrated [10][11][12][13][14][15] that the amount of protonated ions generated by a thermally induced proton transfer reaction has an order of magnitude similar to that observed in experimental measurements.…”

Section: Introductionsupporting

confidence: 62%

“…Many studies on MALDI have discussed the procedures involved in generating these protonated peptides and proteins [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Carbohydrate ions are generated in MALDI as sodiated or potassiated carbohydrates.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, we proposed a thermal proton transfer model to describe the generation of protonated ions in MALDI [10][11][12][13][14][15]. The absorption of laser light by matrix molecules results in an increased temperature, and the solid matrix melts and behaves in a similar manner to a polar solvent before the occurrence of desorption.…”

Section: Introductionmentioning

confidence: 99%

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Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization

Lee

Hsu

et al. 2016

J. Am. Soc. Mass Spectrom.

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Abstract. In a study of the metal-related ion generation mechanism in matrix-assisted laser desorption ionization (MALDI), crystals of matrix used in MALDI were grown from matrix-and salt-containing solutions. The intensities of metal ion and metal adducts of the matrix ion obtained from unwashed crystals were higher than those from crystals washed with deionized water, indicating that metal ions and metal adducts of the matrix ions are mainly generated from the surface of crystals. The contributions of preformed metal ions and metal adducts of the matrix ions inside the matrix crystals were minor. Metal adducts of the matrix and analyte ion intensities generated from a mixture of dried matrix, salt, and analyte powders were similar to or higher than those generated from the powder of dried droplet crystals, indicating that the contributions of the preformed metal adducts of the matrix and analyte ions were insignificant. Correlation between metal-related ion intensity fluctuation and protonated ion intensity fluctuation was observed, indicating that the generation mechanism of the metal-related ions is similar to that of the protonated ions. Because the thermally induced proton transfer model effectively describes the generation of the protonated ions, we suggest that metal-related ions are mainly generated from the salt dissolution in the matrix melted by the laser.

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Section: Introductionsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

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Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization

Lee

Hsu

et al. 2016

J. Am. Soc. Mass Spectrom.

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“…[3][4][5][6][7][8][9][10][11] It is important to recognize that the MALDI process is governed by ablation (or desorption) induced by photophysical or acoustical process being the major event, while the ionization is a minor event having the values of ion-to-neutral ratio (I/N) in the range of 10 −5 to 10 −3 for analyte with good ion intensity, and 10 −9 to 10 −7 for matrix or total species. 10,11) e most basic phenomenon in the MALDI events is the formation of matrix neutral/ionic species, such as M · , H · , M 12,13) e formation of neutral matrix radicals M · and hydrogen atoms H · is a rather major event than ion formation. 12,13) e hydrogen atoms can bring about reductive reactions resulting in hydrogenated radical ions such as [M+2H] · + of 2,5-dihydroxybenzoic acid (2,5-DHB) and 3-aminopyrazine-2-carboxylic acid.…”

Section: Introductionmentioning

confidence: 99%

Photochemical Reactions of Aminonaphthols Caused by Laser Desorption/Ionization

et al. 2016

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e formation of monomeric and dimeric ions of seven di erent aminonaphthols (ANLs) has been studied by using laser desorption/ionization (LDI) with a nitrogen laser. e positive-ion data of all the ANLs merely showed molecular ion M · + without protonated molecule [M+H] + , while 1-amino-2-naphthol (1,2-ANL) and 2-amino-1-naphthol (2,1-ANL) showed an intense dimeric ion [2 M−2H 2 O+H] + . e negativeion data showed deprotonated molecule [M−H] − in common, while the spectra of 1,2-ANL, 2,1-ANL and 8-amino-2-naphthol (8,2-ANL) accompanied an intense peak corresponding to negative molecular ion M · − and the 8,2-ANL and 4-amino-1-naphthol (4,1-ANL) accompanied dehydrogenated anion [M−2H] · − . e formation of monomeric ions was discussed from the standpoints of thermochemical properties such as ionization energy, gas-phase acidity, electron a nity, and bond dissociation energy. e formation of dimeric ions [2 M−2H 2 O+H] + observed in the 1,2-ANL and 2,1-ANL could be explained by the radical combination in the amino groups. An isomer 5-amino-1-naphthol (1-ANL) did not give any dimeric ions in the both positive-and negative-ion spectra. e in uence of laser uence upon the appearance of the monomeric ions such as M

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“…24 However, it should further be pointed out that the finite optical penetration depth (100 nm) and significant differences in surface temperature (facing analyzer input) will too contribute to both the observed higher threshold fluence and velocity distribution. 29 Nevertheless, it was shown that the spectra are still in quantitative agreement for both geometries, especially with regards to mass resolution and analyte fragmentation.…”

mentioning

confidence: 98%

Femtosecond Pumping Rate Dependence of Fragmentation Mechanisms in Matrix-Assisted Laser Desorption Ionization

Pieterse

Busse

Tellkamp

et al. 2018

Preprint

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The benzyltriphenylphosphonium (BTP) thermometer ion is utilized to characterize the fragmentation mechanisms of matrix-assisted laser desorption/ionization (MALDI) for femtosecond ultraviolet laser pulses. We demonstrate that the survival yield of BTP approaches unity under these conditions, which suggests that a minimal amount of fragmentation is occurring. It is also shown that the survival yield of BTP is insensitive to the laser fluence. However, the magnitude of fragmentation for the matrix increased notably for the same fluence range. These results indicate that the amount of energy transferred from the matrix ions to the BTP thermometer ions is minimal because the femtosecond desorption applied here occur within the stress-confinement regime. This observation is in agreement with recent molecular dynamics simulations which predict that it should be possible to separate both desorption and ionization processes in the regime of stress-confined desorption. Our results indicate that angiotensin is the largest biomolecule which could be routinely measured with these pulses. A mass upper-limit supports the hypothesis that ionization is hindered by the increased thermal gradients imposed in the lattice and associated velocity distribution within the ablation process from the much higher lattice heating rate with femtosecond pulses. This effect results in the temporal overlap between the neutral molecules and the matrix ions being too small to result in sufficient proton exchange for ionization. Graphical TOC Entry2

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Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization

Cited by 60 publications

References 59 publications

Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization

Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization

Photochemical Reactions of Aminonaphthols Caused by Laser Desorption/Ionization

Femtosecond Pumping Rate Dependence of Fragmentation Mechanisms in Matrix-Assisted Laser Desorption Ionization

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