Effects of Matrix Structure/Acidity on Ion Formation in Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

Gimon-Kinsel, Mary E.; Preston-Schaffter, Lisa M.; Kinsel, Gary R.; Russell, David H.

doi:10.1021/ja960269b

Cited by 41 publications

(27 citation statements)

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“…Peptides that did not contain aromatic amino acids had the lowest EIP values at less than 6%. These results were again consistent with efficient ionization of UV absorbing aromatic amino acid aerosols, and substituted aromatic compounds ionized from a surface as in MALDI [26].…”

Section: Analyses Of Single Component Particles Of Peptidessupporting

confidence: 76%

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

Russell

Czerwieniec

Lebrilla

et al. 2004

J. Am. Soc. Mass Spectrom.

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The appearance of informative signals in the mass spectra of laser-ablated bio-aerosol particles depends on the effective ionization probabilities (EIP) of individual components during the laser ionization process. This study investigates how bio-aerosol chemical composition governs the EIP values of specific components and the overall features of the spectra from the bio-aerosol mass spectrometry (BAMS). EIP values were determined for a series of amino acid, dipicolinic acid, and peptide aerosol particles to determine what chemical features aid in ionization. The spectra of individual amino acids and dipicolinic acid, as well as mixtures, were examined for extent of fragmentation and the presence of molecular ion dimers, which are indicative of ionization conditions. Standard mixtures yielded information with respect to the significance of secondary ion plume reactions on observed spectra. A greater understanding of how these parameters affect EIP and spectra characteristics of bio-aerosols will aid in the intelligent selection of viable future biomarkers for the identification of bio-terrorism agents. (J Am Soc Mass Spectrom 2004, 15, 900 -909)

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Section: Analyses Of Single Component Particles Of Peptidessupporting

confidence: 76%

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

Russell

Czerwieniec

Lebrilla

et al. 2004

J. Am. Soc. Mass Spectrom.

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“…Russell and co-workers focused on the possible role of ESPT in the gas phase. 1 They pointed out that the gas-phase and especially the excited-state acidity of the protonated matrix molecule may be very different from the value we assign based on chemistry in aqueous solutions. Studying para-substituted aniline compounds as matrices, they concluded that the carboxyl hydrogen, common to the most efficient UV MALDI matrices, is not necessarily the source of the transferred proton.…”

Section: Introductionmentioning

confidence: 67%

Protonation of Gly_n Homologues in Matrix-Assisted Laser Desorption Ionization

Olumee

Vertes

1998

J. Phys. Chem. B

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Protonation reactions of Gly n homologues were studied in order to elucidate the effect of peptide chain length and matrix materials on the matrix-assisted laser desorption ionization (MALDI) mechanism. At 337 nm nitrogen laser excitation the relative ion yield-chain length relationship showed considerable variability in 3,5-dimethoxy-4-hydroxycinnamic acid (SA), 2,5-dihydroxybenzoic acid (DHB), 6-aza-2-thiothymine (ATT), and R-cyano-4-hydroxycinnamic acid (CHCA), the four matrices studied. For SA and ATT, a monotonic increase of relative ion yields (RIYs) was observed with increasing peptide length. Similar increasing pattern and significantly higher RIYs were found for the homologues of the Gly n series in the CHCA matrix with the exception of Gly. The particularly high MALDI ion yield of this amino acid in CHCA may be attributed to preferential embedding and/or more efficient condensed-phase proton transfer. To unveil the nature of the proton-transfer reactions in MALDI, the peptide length dependence of the measured RIYs was compared to the trends observed in proton affinities (PAs) of the same homologues as well as to ion-molecule reaction rates calculated using the Langevin cross section. Chain extension enhancements in MALDI RIYs of all the studied matrices cannot be explained either by the increase in ground-state ion-molecule reaction rates or by a linear dependence on gas-phase PAs. However, in SA and ATT positive correlation was observed between MALDI RIYs of Gly n homologues and their PAs. The RIYs observed in CHCA were significantly higher than in SA. This effect could be explained by the markedly lower PA of CHCA (183 ( 2 kcal/mol) compared to that of SA (204 ( 4 kcal/mol).

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“…On the other hand, negative matrix ions may be produced by the attachment of low-energy electrons during material desorption processes, as reported previously by Pshenichnyuk and coworkers [29 -31]. However, many papers proposed that the initial matrix ions may produced by the disproportionation of protons or electrons between adjacent matrix molecules, which involves the production of ion-pairs like M ϩ and M Ϫ , or [M ϩ H] ϩ and [M Ϫ H] Ϫ [12,13,26,32], as shown below:…”

Section: Atrix-assisted Laser Desorption/ionizationmentioning

confidence: 75%

Incoherent production reactions of positive and negative ions in matrix-assisted laser desorption/ionization

Liu

Lee

Wang

2009

J. Am. Soc. Mass Spectrom.

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Utilizing synchronized dual-polarity matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, we found good evidence of the incoherent production of positive and negative matrix ions. Using thin, homogeneous 2,5-dehydroxybenzoic acid (DHB) matrix films, positive and negative matrix ions were found to appear at different threshold laser fluences. The presence of molecular matrix ions of single charge polarity suggests that the existence of DHB ion-pairs may not be a prerequisite in MALDI. Photoelectrons induced by the laser excitation may assist the production of negative DHB ions, as shown in experiments conducted with stainless steel and glass substrates. At high laser fluences, the relative yield of positive and negative matrix ions remained constant when homogeneous matrix films were used, but it fluctuated significantly with inhomogeneous crystal morphology. This result is also inconsistent with the hypothesis that matrix ion-pairs are essential primary ions. (MALDI) provides a convenient means to produce protein and peptide ions for mass analysis [1, 2], but its application to the studies of biopolymers such as carbohydrates is still limited by insufficient ion yields [3,4]. It is generally accepted that the protonated matrix molecules are the essential initial ions responsible for the production of positively-charged analytes [5], normally via proton transfer reactions. But such a qualitative description is insufficient to provide guidelines for the optimization of experimental conditions for the wide variety seen in biological samples. The paucity of our knowledge of detailed ionization mechanisms makes the optimization of MALDI performance a highly empirical process and thus the primary bottleneck of this method. In the last decade, Karas and coworkers and Knochenmuss and coworkers have respectively established a cluster model [6,7] and a two-step model [8 -10] to explain MALDI. The two models are divergent in several aspects, including the origin of the initial ions that trigger the subsequent reactions, the role of ion-neutral reactions during material desorption, the contribution of photoelectrons in the reactions, etc. The two reaction models seem not converge over time mainly due to the insufficient information provided by conventional mass spectrometric methods. It is thus desirable to develop our understanding of MALDI from novel perspectives, such as the correlation between primary positive and negative ions at the time of ionization.A recent report based on a synchronized dual-polarity MALDI-TOF method stated that the spectral pattern of MALDI-generated positive ions were approximately equal to those of the negative ions for some moderate-size proteins [11]. There was thus some speculation over whether the positive and negative ions are produced in a pair-wise fashion in MALDI [12,13], or whether they are the result of preformed ion-pairs in the crystal before laser irradiation [6]. More recently, Dashtiev and coworkers [14] systemically studied the correlation of positive and ne...

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Effects of Matrix Structure/Acidity on Ion Formation in Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

Cited by 41 publications

References 50 publications

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

Protonation of Gly_n Homologues in Matrix-Assisted Laser Desorption Ionization

Incoherent production reactions of positive and negative ions in matrix-assisted laser desorption/ionization

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Effects of Matrix Structure/Acidity on Ion Formation in Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

Cited by 41 publications

References 50 publications

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

Toward understanding the ionization of biomarkers from micrometer particles by bio-aerosol mass spectrometry

Protonation of Glyn Homologues in Matrix-Assisted Laser Desorption Ionization

Incoherent production reactions of positive and negative ions in matrix-assisted laser desorption/ionization

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Protonation of Gly_n Homologues in Matrix-Assisted Laser Desorption Ionization