Applications of MALDI-MS

Although not a common practice, quantification of a range of molecules, especially of peptides, has been performed with MALDI-MS [14-18]. A major 

MALDI has also been used to quantify small molecules. This aspect has been demonstrated by the analysis of lysergic acid diethyl amide (LSD) with atmospheric pressure (AP) MALDI [20]. LSD is a hallucinogen. Its quantification is highly important from forensic and clinical point of views. In this method, LSD was extracted and precleaned from urine samples by SPE and quantified by recording the ion current due to m/z 327 226 and 324 223 transitions. The standard curves were plotted by analyzing several LSD standard solutions, each of which was spiked with LSD-iis as an IS. A linear calibration curve was obtained over the concentration range 1 to 100 ng mL with = 0.9917. The results were comparable with those of an existing HPLC/ESI-MS method. 

In this chapter, quantitative applications of mass spectrometry were discussed. In this respect, mass spectrometry is distinctly superior over most other analytical techniques. Mass spectrometry-based methods are more specific and highly sensitive. In combination with high-resolution separation devices, the task of quantitation of real-world samples becomes much easier. A mass spectrometry signal is acquired in the SIM or SRM mode. In SIM, the ion current due to one or more compound-related ions is recorded, whereas in SRM, precursor-product 

For precise and accurate quantification, it is essential to obtain a calibration curve to accurately define the relation between a known concentration of the analyte and the mass spectrometry signal. Calibration is performed with the external calibration, standard addition, or internal standard method. The last method is more accurate because an internal standard can account for deviation in the mass spectrometry response and the sample losses that might occur in various samplehandling and chromatographic steps. An internal standard is any compound that has chemical and physical properties similar to those of the analyte or homologous to the analyte or a stable isotope-labeled analog of the analyte. The last type of standard provides more accurate results because its chemical and physical properties are virtually identical to those of the analyte. 

Any newly developed method must be validated according to the acceptable criteria. To validate a method, LOD, LOQ, linear range, specificity, precision and accuracy, specificity, and robustness of the method should be determined. 

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HPLC and the extensive complexity of ESI and MALDI spectra for multicomponent polymers with molar mass over about 10 g mol. Some applications of MALDI MS in polymer HPLC can be found for example in [300-303],... 

As was first described in 1997 [4], the application of MALDI MS to the direct analysis of proteins in tissue sections is illustrated in Figure 12.1. The general procedure is to obtain a thin section of a sample of interest, apply matrix (which is necessary for the MALDI process), and then acquire mass spectra at discrete x-, y-coordinates over the entire sample section. Each individual mass spectrum contains signals corresponding to proteins (and other endogenous compounds, including peptides, lipids, and metabolites) present in the sample at a unique set of coordinates. The intensities of any given molecular species may then be plotted as a function of position on the sample surface. 

Zhao, I.Y. et al., Application of MALDI-MS/MS molecular imaging software for small molecule profiling in tissue samples, Proceedings of the 51st ASMS Conference, Montreal, Quebec, Canada, 2003. 

Table 1.5A. Application of MALDI-MS profiling of mass-limited tissue and single cell samples [Refs in 49].

Here, we will describe a range of applications of MALDI-MS, from the concepts of in-depth analysis of purified proteins to applications of MALDI-MS in a broader, proteomics-based research where proteins are identified, characterized, and quantified. In addihon, issues of sample preparation, protein characterization and identification strategies and bioinformatic tools for data interpretation wiU be discussed. The concepts of peptide fragmentation, sequencing and derivatization, analysis of post-translational modifications and the clinical apphcations of MALDI-MS are also briefly outlined. 

As for protein chemistry and proteomics studies, sample preparation is a critical issue in the clinical application of MALDI-MS. In this context, sample preparation... 

MALDI-MS transforms the practice of polymer characterization [8-12], and today has become a widely used technique for the analysis of a huge variety of polymers [6]. There are several unique attributes of MALDI-MS which, together, make it a powerful technique for polymer characterization. In this chapter, these attributes will be discussed, along with many technical issues related to the use of MALDI-MS for polymer characterization. A few selected applications of MALDI-MS and MS/MS will also be outlined in order to illustrate the power of the technique in solving practical problems. This chapter does not aim to survey all published studies in the area of MALDI polymer characterization rather, it attempts to provide an overview on the technique, attributes, and current limitations of MALDI-MS for polymer analysis. 

A number of pubUcations have demonstrated the applications of MALDI-MS for polymer characterization. Of particular interest, Hanton provided a Ust of pubUcations summarized according to the type of polymers analyzed by MALDI-MS [11]. In addition, an updated web-based resource for polymer/matrix preparation protocols is available from the Polymers Division of the National Institute of Standards and Technology (NIST) homepage (http //polymers.msel.nist.gov/ maldirecipes). 

Finally, whilst attention has been focused on profiling applications in a clinical setting, the bioinformatics and statistics methods described in this chapter are general and applicable for other applications of MALDI-MS, using different types of mass analyzers such as Fourier transform ion cyclotron resonance mass sp>ec-trometers and Orbitrap platforms. 

This is a last minute add-on chapter. It is not as comprehensive as the other chapters, but the editors considered it important, because it is the first and so far only large scale routine clinical application of MALDI MS. The application has boomed over the last two years and is still in a phase of intense development. The most important aspects of this new application are discussed in the chapter for details, readers are referred to the many listed references. 

Revisions in Chapter 7 are related to the increased interest in lipid analysis, notably boosted by introduction of the new omics field-lipidomics-and by developments of MS imaging as a robust new application of MALDI-MS. In addition, novel potentials of lipid analysis in applications of the direct desorption from solid surfaces and MALDl-MS imaging to diagnostics using Upids as disease markers are described. 

By the application of MALDI-MS, precise information on the size, structure, and end groups of oligomers origi-... 

An excellent, timely review regarding applications of MALDI MS to characterize glycosphingolipids (GSL) has been recently published [34] and this is the reason why we will mention here only a few selected highlights. In an early MALDI attempt [35], native GSL were separated on a conventional (silica gel 60) TLC plate by using... 

Advances in methods used in the structural characterisation of redox-active polymers will aid in developing structure/property relationships and in guiding synthetic efforts. MALDI-MS analysis has proved to be a powerful structural characterisation tool for biopolymers. The application of MALDI-MS to synthetic polymers has been primarily limited to polar or polarisable polymers that can be protonated or can form salt/metal adducts. Electron transfer matrices for MALDI-MS of small, non-polar, redox-active analytes have been evaluated and it was found that anthracene and terthiophene are effective MALDI matrices for these analytes and assist in producing analyte molecular ions (not protonated molecules). Thus, non-polar, redox-active polymers might also be similarly ionised. 

MALDI-MS is generally performed at (complex) lipids mixtures, although post-LC-column fractionation systems have been developed as well. Additionally, MALDI-MS imaging of TLC plates is useful technology in Upid analysis [219]. The application of MALDI-MS in lipid analysis and lipidomics has been extensively reviewed [193, 194, 220, 221]. The most widely applied matrices in lipid analysis are DHB and 2,6-dihydroxyacetophenone (DHAP). Unlike in ESI-MS, MALDI-MS provides positive-ion response for all phospholipid classes. Individual components may be observed as [M+H]+, [M+Na], [M+K]+, or adduct ions with additional HWa - or H+/K+-exchange, thus significantly complicating the interpretation and (relative) quantification of individual components in... 

MALDI polymer analysis consists of three steps, namely sample preparation, mass spectral recording, and data analysis. Matrices and sample preparation are crucial points for the applicability of MALDI-MS. The analyte molecules, often a polymer, are dispersed in a matrix of small organic molecules with strong optical absorption at the desorption laser wavelength. In this way desorption/ionisation of the analyte molecules can be achieved regardless of their absorption properties. The sample is prepared by... 

MALDI applications are growing at a rapid pace with over 3000 publications annually since 2006 (Fig. 11.18). A single book chapter thus can impossibly cover all aspects of these developments. However, there are several excellent monographs on different aspects of MALDI which are highly recommended to anyone intending to pursue further studies of MALDI-MS [15,23,143-145]. The following section will merely outline some flagship applications of MALDI-MS. 

Applications of MALDI-MS to polymer degradation are quite recent [152-160]. The study involves the collection of MALDI spectra of samples degraded at different... 

The comparability of MALDI results obtained in different laboratories can only be ensured by using standardized conditions of measurement, and identical sample and matrix preparation methods. Therefore, national and international MALDI-TOF MS round robin tests have been jjetfotmed. Their results were used to create national and international norms (ASTM, DIN, and ISO) for the determination of molecular masses and mass distributions of important polymer classes (PS, PMMA, and PEO). The classification of MALDI as an equitable (standardized) method relating to other established methods of polymer characterization may give an important push for increasing the application of MALDI MS. 

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