Electron capture negative ion mass spectra of some typical matrix‐assisted laser desorption/ionization matrices

Asfandiarov, N. L.; Pshenichnyuk, S. A.; Fokin, A. I.; Lukin, V. G.; Fal’ko, Vladimir I.

doi:10.1002/rcm.787

Cited by 29 publications

(29 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Such counter parts may be the metal substrates, bottom-layer matrices, or big chunks of matrix clusters that are not visible in MALDI spectra, as proposed elsewhere in the literature [14,41]. Therefore, the production of m-negative ions may proceed via electron-attachment reactions [29,31] because the ejection of both neutral molecules and photoelectrons occurred at fluences lower than the ion appearance threshold [42].…”

Section: Appearance Thresholds Of Ions (Low Laser Fluence)mentioning

confidence: 94%

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

Liu

Lee

Wang

2009

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

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...

show abstract

Section: Appearance Thresholds Of Ions (Low Laser Fluence)mentioning

confidence: 94%

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

Liu

Lee

Wang

2009

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

“…These models are concerned with the formation of M +• (together with an electron) (28), which may be converted into [M + H] + . Also, electron capture by M may produce M −• (29), which can be further converted into [M − H] − . Because the efficiencies of these reactions would differ widely, it is unlikely that the primary cations and anions will have similar abundances.…”

Section: Abundances Of the Primary Cations Anions And Photoelectronmentioning

confidence: 99%

A Thermal Mechanism of Ion Formation in MALDI

Bae

Kim

2015

Annual Rev. Anal. Chem.

View full text Add to dashboard Cite

An important recent discovery concerning the fundamentals of matrix-assisted laser desorption/ionization (MALDI) is that the abundance of each ion appearing in a spectrum is fixed, regardless of the experimental condition, when an effective temperature associated with the spectrum is fixed. We describe this phenomenon and the thermal picture for the ion formation in MALDI derived from it. Accepting that matrix-to-analyte proton transfer is in quasi-equilibrium as supported by experimental data, the above thermal determination occurs because the primary (matrix) ion formation processes are thermally governed. We propose that the abundances of the primary ions are limited by the autoprotolysis-recombination process regardless of how they are initially produced. Finally, we note that primary ion formation, secondary (analyte) ion formation, and their dissociations occur sequentially while the effective temperature of the matrix plume falls steadily due to cooling associated with expansion.

show abstract

“…53 In addition, deprotonated matrix can also be formed by electron capture of neutral matrix molecules. 54 All these factors complicate the correlation between the protonation and the cationization of analyte.…”

Section: Cationization Vs Protonation/deprotonationmentioning

confidence: 99%

Matrix‐dependent cationization in MALDI mass spectrometry

Zhang¹,

Zenobi²

2004

J. Mass Spectrom.

View full text Add to dashboard Cite

The matrix dependence in cationization processes, the competition between cationization and protonation and the question of whether gas-phase cation transfer or attachment of free cations dominates in matrix-assisted laser desorption/ionization mass spectrometry were studied. Two different sample preparation methods were employed, the dried-droplet sample preparation and a mixture of solid matrix, analyte and salt. The latter ensures that the formation of cation adducts takes place in the gas phase. By monitoring the suppression of matrix signals for different matrices, it was found that matrices with high gas-phase metal ion binding energies require high analyte concentrations for matrix suppression to occur. By comparing the mass spectra obtained using sinapinic acid or sinapinic methyl ester as a matrix, a correlation between cationization and deprotonation of matrix molecules was found. It is also demonstrated that attachment of free gas-phase cations, rather than cation transfer from the cationized matrix, is the predominant process in cationization.

show abstract

Electron capture negative ion mass spectra of some typical matrix‐assisted laser desorption/ionization matrices

Cited by 29 publications

References 16 publications

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

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

A Thermal Mechanism of Ion Formation in MALDI

Matrix‐dependent cationization in MALDI mass spectrometry

Contact Info

Product

Resources

About