Extending the solvent-free MALDI sample preparation method

Hanton, Scott D.; Parees, David M.

doi:10.1016/j.jasms.2004.09.019

Cited by 87 publications

(114 citation statements)

References 16 publications

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“…The vortex method [16] involves adding the dry components of the analyte (about 0.1-0.2 mg), matrix (20 -40 mg), and cationization agent (trace to 0.1 mg) to a small glass vial. We typically add the analyte first, followed by the matrix and then the cationization agent, but there is no clear reason why the order of addition would matter to these experiments.…”

Section: Sample Preparation: Vortex Methodsmentioning

confidence: 99%

“…While several groups investigated solventfree sample preparation methods at nearly the same time, the methods developed by Trimpin, Räder, and coworkers have gained widespread use [11][12][13][14][15]. To make the sample preparation step easier, less time consuming, and reduce the risk of cross-contamination, we developed a simple version of the solvent-free sample preparation method, now called the vortex method [16]. Although the utility of solvent-free sample preparation for MALDI has been clearly demonstrated, the investigations into why it works and what impact these data have on our overall understanding of the MALDI process have only recently begun [17,18].…”

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confidence: 99%

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Imaging the morphology of solvent-free prepared MALDI samples

Hanton

McEvoy

Stets

2008

J. Am. Soc. Mass Spectrom.

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Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is an important technique to characterize many different materials, including synthetic polymers. MALDI mass spectral data can be used to determine the polymer average molecular weights, repeat units, and end groups. The development of solvent-free sample preparation methods has enabled MALDI to analyze insoluble materials and, interestingly, can provide higher-quality mass spectral data. Although the utility of solvent-free sample preparation for MALDI has been demonstrated, the reasons for its success are only now being discovered. In this study, we use microscopy tools to image samples prepared using solvent-free methods to examine the morphology of these samples. The samples are prepared using a simple vortex method. Our results show that the average particle size of typical MALDI matrices is reduced from their original tens to hundreds of micrometers to hundreds of nanometers. This size reduction of the matrix occurs in one minute using the vortex method. We also observe remarkably smooth and homogeneous sample morphologies for the laser to interrogate, especially considering the relatively crude methods used to prepare our samples. [5][6][7][8][9][10]. MALDI can generate important data on the telomer repeat units, end groups, and average molecular weights of these materials. MALDI methods have been developed to address a broad variety of different polymer materials containing different chemistries. One of the key issues in traditional MALDI sample preparation is making true solutions of the analyte and the matrix [9]. Many interesting polymeric analytes are either completely insoluble or present significant challenges in making analytically useful solutions. To address these issues, solvent-free sample preparation methods have been developed. While several groups investigated solventfree sample preparation methods at nearly the same time, the methods developed by Trimpin, Räder, and coworkers have gained widespread use [11][12][13][14][15]. To make the sample preparation step easier, less time consuming, and reduce the risk of cross-contamination, we developed a simple version of the solvent-free sample preparation method, now called the vortex method [16]. Although the utility of solvent-free sample preparation for MALDI has been clearly demonstrated, the investigations into why it works and what impact these data have on our overall understanding of the MALDI process have only recently begun [17,18].To develop increased understanding of the utility of the solvent-free MALDI sample preparation method, we have investigated the morphology of these samples using different imaging experiments-optical imaging [19], scanning electron microscopy (SEM) [20], atomic force microscopy (AFM) [21], and time-of-flight secondary ion mass spectrometry (ToF-SIMS) [22]. Previous work has shown the utility of investigating MALDI sample morphology using imaging methods. We have used SEM to investigate the morphology of electrospray deposited samples [23] ...

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Section: Sample Preparation: Vortex Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Imaging the morphology of solvent-free prepared MALDI samples

Hanton

McEvoy

Stets

2008

J. Am. Soc. Mass Spectrom.

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“…Solvent-free or dry prepared sample methods have also been developed and show some advantages over traditional wet sample preparation methods [28]. For example, solvent-free sample preparation methods enable analysis of insoluble materials and reportedly provide higher quality mass spectra.…”

Section: Modifications To the General Maldi Approachmentioning

confidence: 99%

Quantitative matrix-assisted laser desorption/ionization mass spectrometry

Duncan¹,

Röder²,

Hunsucker³

2008

Briefings in Functional Genomics and Proteomics

191

162

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This review summarizes the essential characteristics of matrix-assisted laser desorption/ionization (MALDI) timeof-flight mass spectrometry (TOF MS), especially as they relate to its applications in quantitative analysis. Approaches to quantification by MALDI-TOF MS are presented and published applications are critically reviewed.Keywords: quantification; quantitative analysis; MALDI; mass spectrometry; biomarkers OVERVIEWSince its inception in 1987 [1], matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry (TOF MS) has been applied for the analysis of a wide range of biomolecules. Initial applications were almost exclusively for the qualitative analysis of biopolymers because MALDI-TOF MS provided a fast and accurate approach to molecular mass and purity information: Is my material the right mass and is it free from contaminants? Because of the speed of analysis, ease of use, relative low equipment cost, ease of data interpretation and limited potential for cross-contamination between samples/users, MALDI-TOF MS systems were considered walk-up instruments where investigators run their own samples and determine, within minutes, whether they were on the right track with their work.There were, however, two specific areas of application where MALDI-TOF MS was initially viewed as impractical: i.e. the analysis of low mass analytes and quantitative applications. Low mass analysis is complicated by the vast molar excess of the matrix that can swamp any analyte-specific signal in the low m/z region of the spectrum. Quantitative analysis was viewed as implausible because crystallization does not yield a uniform distribution of the analyte and matrix across the target surface and this gives rise to regions where the analyte signal is especially intense relative to other locations on the target surface. MALDI MS was therefore viewed as inherently irreproducible because, for a given amount of analyte loaded onto the target, the measured ion intensity varies.Subsequently, it has been shown that both these perceived limitations can be overcome and quantification can be routine, both for low and high mass analytes. Now, an extensive list of published applications includes quantification of amino acids, lipids, natural products, drugs, polymers, herbicides, metabolites, toxins, oligonucleotides, carbohydrates, peptides and proteins. (Selected applications from these areas are discussed at the end of this review.) Here, we focus on the quantitative applications of MALDI and illustrate applications relating to both low and high-molecular mass analytes. We also discuss the strategies for applying MALDI to relative and absolute quantification. While MALDI is most commonly combined with TOF analysers, other analyser options are possible and applications employing these are also presented. Our aim is not to provide an exhaustive catalogue of published applications, but to discuss the general principles and to illustrate the

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“…The following combinations of matrix/solvent/cationizing agent were tested: dithranol or all-trans retinoic acid/THF or dichloromethane or toluene/silver nitrate or silver trifluoroacetate. An alternative solvent-free preparation method [31][32][33] was modified and also tried as described below.…”

Section: Sample Preparationmentioning

confidence: 99%

“…For the solvent-free sample preparation [31][32][33], a small pellet of polystyrene was combined with the matrix in 10:1 to 1000:1 matrix-to-analyte ratio and 1% by mass of silver nitrate and pulverized in a mill (Tokken, Inc., Chiba, Japan) that consisted of a stainless steel plunger inside a plastic vial. The dry mixture was then pressed onto a MALDI plate with a spatula for MALDI analysis.…”

Section: Sample Preparationmentioning

confidence: 99%

The analysis of polystyrene and polystyrene aggregates into the mega dalton mass range by cryodetection MALDI TOF MS

Aksenov

Bier

2008

J. Am. Soc. Mass Spectrom.

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Mass spectra of atactic polystyrene were collected into the mega-dalton mass range with a matrix-assisted laser desorption ionization time of flight (MALDI TOF) mass spectrometer, which incorporates a cryodetector comprised of an array of 16 superconducting tunnel junctions (STJ). The STJ cryodetector, theoretically, has no loss in signal response at any mass compared with the reduced signal found at high mass when using a conventional secondaryionization detector. Since ion detection at high m/z is one of the fundamental limitations of mass spectrometry (MS), the cryodetector was used to explore the high m/z limit of the MALDI TOF technique for the analysis of two polymer types. Mass spectra were collected for polystyrene at M n 170, 400, 900, and 2000 kDa and polymethyl methacrylate (PMMA) at M n 62.6 kDa and 153.7 kDa. For polystyrene, the data showed a trend toward increased aggregation and charge state with mass. The M n 2 MDa polystyrene data revealed a peak at m/z 2.2 MegaTh and a charge state analysis revealed that these ions were primarily polystyrene aggregates with a mass of ϳ4 MDa. This aggregate assignment was possible because the cryodetector response allows for the determination of a charge state up to about four. The contribution of each charge state for a selected peak can be determined in this fashion. This analysis revealed the preferential formation of doubly charged even-numbered aggregates over oddnumbered aggregates for high molecular mass polystyrene. A potential mechanism for the aggregation process for doubly charged species is discussed. Karas and Hillenkamp [3]. The MALDI technique was a major breakthrough in mass spectrometry and it has seen widespread use in chemical and biological research because it offers several key advantages. First, it is a relatively "soft" ionization technique that can produce intact low charge state molecular ions at low laser power. Second, like electrospray ionization (ESI), MALDI is suitable for the ionization of large nonvolatile molecules including synthetic polymers and biomacromolecules, which cannot be brought into the gas phase and ionized intact by most other more energetic introduction and ionization techniques. Third, the MALDI technique is more robust than ESI for samples that contain high concentrations of salts and buffers. And finally, because MALDI can be operated in a pulsed ionization mode, it can be conveniently coupled to a time-of-flight (TOF) mass spectrometer. The theory and applications of the MALDI method are reviewed elsewhere [4 -6].It is reasonable to assume that the MALDI technique may have an upper m/z limitation. For example, the laser desorption ionization (LDI) technique, is limited to ϳ1000 Da for intact biological molecules and a few kDa for synthetic polymers [7]. Compared with LDI, MALDI shows reduced fragmentation of macromolecules [8] and the mass range has been extended to several 100 kDa. This extension of the mass range is attributed to the abundant matrix, usually in a ratio of at least 1000:1 with the analyte th...

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Extending the solvent-free MALDI sample preparation method

Cited by 87 publications

References 16 publications

Imaging the morphology of solvent-free prepared MALDI samples

Imaging the morphology of solvent-free prepared MALDI samples

Quantitative matrix-assisted laser desorption/ionization mass spectrometry

The analysis of polystyrene and polystyrene aggregates into the mega dalton mass range by cryodetection MALDI TOF MS

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