Secondary ion-molecule reactions in matrix-assisted laser desorption/ionization

Knochenmuss, Richard; Stortelder, Aike; Breuker, Kathrin; Zenobi, Renato

doi:10.1002/1096-9888(200011)35:11<1237::aid-jms74>3.0.co;2-o

Cited by 162 publications

(223 citation statements)

References 65 publications

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“…The ions observed in each polarity were found to be dependent on the relative acidities and basicities of the components in the mixture. The presence of protonated DPA and Phe in the single component particles but not in mixtures with Arg indicate a competition that likely occurs during the desorption/ionization process, a process similar to that believed for MALDI [20,27]. These results also explain a number of observations in the analyses of the spores.…”

Section: Discussionsupporting

confidence: 59%

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: Discussionsupporting

confidence: 59%

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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“…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: 76%

“…Although it has been claimed that the MALDI mass spectra may not reveal useful primary ionization mechanisms [24,32], new insight into these mechanisms may still be extracted from the correlation of spectral features between two opposite polarities. The present work focuses on a simple condition where no guest (analyte) molecules are involved, thus the charged species should associate only with the matrix and should be eventually detected.…”

Section: Resultsmentioning

confidence: 99%

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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“…The most current representation is the energy transfer-induced disproportionation model that considers that a pseudo-proton transfer occurs during the crystallization process in MALDI sample preparation (65). Other publications claim that the final, detected mass spectrum is in many cases predominantly determined by secondary reactions that occur in the MALDI plume (29,47,59).…”

mentioning

confidence: 99%

Investigating the Quantitative Nature of MALDI-TOF MS

Szaéjli

Feheér

Medzihradszky

2008

Molecular & Cellular Proteomics

138

116

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MALDI-TOF MS has been applied by several groups to relative quantitative measurements. At the same time, the non-quantitative character of this method has been widely reported. We conducted experiments to test the reliability of this technique for quantitation using the statistical method of inverse confidence limit calculation for the first time in this context. The relationship between relative intensities of known amounts of standard peptides and their concentration ratios was investigated. We found that the concentration ratios determined by relative intensity measurements were highly inaccurate and strongly influenced by the molecular milieu of the sample analyzed. Thus, we emphasize the necessity of using the sample itself for calibration. We also performed experiments using an isotope-labeled derivative of the analyte as an internal standard for calibration line generation. As expected, the use of such standard led to a dramatic increase in precision and a less pronounced improvement in accuracy. We recommend performing a similar statistical analysis as a demonstration of reliability for every system where MALDI-TOF MS is used for quantitative measurements. Molecular & Cellular Proteomics 7: 2410 -2418, 2008.MALDI-TOF MS is a widely used analytical technique because of its excellent sensitivity, relatively high speed, and simplicity. As a consequence of producing mostly singly charged ions (1, 2) MALDI is especially suitable for mixture analysis. It is commonly used in proteomic studies (3) frequently without any prefractionation (4) as well as in the analysis of other biomolecules. Lately MALDI-TOF MS has become a popular method for quantitative analysis of biomolecules (oligonucleotides, proteins, glycoproteins, etc.) originating from various sample types (5-22) or even for imaging tissue sections (13)(14)(15)(16)(17)(18)(23)(24)(25)(26). At the same time, several studies discuss the non-quantitative nature of MALDI-TOF MS (7, 8, 13, 19, 22, 26 -30). The main problem of MALDI is its poor reproducibility (sample to sample and shot to shot), which makes most quantitative measurements quite difficult at best (19,27,31). This is especially true for complex samples. The presence of so-called hot spots or sweet spots is the main cause of the poor reproducibility and is therefore a factor strongly increasing measurement times and complicating automated measurements. Furthermore this phenomenon is one of the major factors hampering the use of MALDI MS for spatially resolved imaging (27). The reasons for sweet spot formation are not completely understood. It could be caused by variation in the amount and the crystallization of the matrix, the latter being a function of local analyte concentration. Dependence of signal intensities on the orientation of the matrix-analyte crystals relative to the spectrometer axis is also possible (27). The extent of hot spot formation depends strongly on the matrix used. For example, preparations with ␣-cyano-4-hydroxycinnamic acid (CHCA) 1 deliver relatively homogenous samples (...

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Secondary ion-molecule reactions in matrix-assisted laser desorption/ionization

Cited by 162 publications

References 65 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

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

Investigating the Quantitative Nature of MALDI-TOF MS

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