Laser desorption/ionization introduction

The introduction and eventual commercialization of matrix-assisted laser desorption/ionization (MALDI) and electrospray (ESI) allowed biomarker status to be extended to proteins in 1996.15"17 With a few exceptions, ESI has been used in conjunction with extractions and high-pressure liquid chromatography (UPLC) interfaced with mass spectrometry. MALDI, on the other hand, has been widely adapted for rapid analysis of intact organisms, supported by bioinformatics.1819... 

The growing interest for the identification and characterization of polar and large compounds caused the development and the introduction of new ionization techniques, such as electrospray ionization (ESI)[4], and matrix assisted laser desorption ionization (MALDI),[5] and their more recent improvements, thus establishing new MS based approaches for studying large molecules, polymers and biopolymers, such as proteins, carbohydrates, nucleic acids. 

Matrix assisted laser desorption ionization (MALDI) Direct insertion probe or continuous-flow introduction. Not easily compatible with LC-MS... 

The introduction of matrices to assist the laser desorption ionization (LDI) process has lead to the development of the so-called matrix-assisted LDI (MALDI). This technique has been applied to identify terpenoid varnishes and their oxidized products [46], Combined with enzymatic cleavage, MALDI has also been used in the identification of animal glue. 

ToF mass spectrometers as dynamic instruments gained popularity with the introduction of matrix assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) as effective pulsed ion sources for the soft ionization of large biomolecules (up to 10s dalton) due to their high ion transmission.38 ToF mass spectrometers, quadrupole analyzers and/or magnetic sector fields can be combined in tandem mass spectrometers (MS/MS) for the analysis of organic compounds. 

In direct introduction the sample can be introduced via a sample probe or plate through a vacuum lock, and can subsequently be ionized via El, Cl or matrix-assisted laser desorption ionization (MALDI see Section 2.4). Alternatively, the sample can be introduced as a liquid stream into an ion source at atmospheric pressure, after which it is subjected to electrospray ionization (ESI see Section 2.3). Direct injection does not offer any form of sample separation. 

FAB and PD have been replaced by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) in the analytical mass spectrometry laboratory, because both of these newer techniques have a wider mass range of analysis and have lower detection limits. ESI and MALDI have become invaluable ionization techniques for nonvolatile components. This is particularly true for a wide range of biological molecules including proteins, peptides, nucleic acids, etc. Samples can be analyzed by ESI using either direct injection or introduction through liquid chromatography. 

Another approach to selenized yeast is to characterize Se-containing proteins. The application of polyacrylamide gel electrophoresis (PAGE) has been proposed with the introduction of the protein spot to ICP-MS via LA or ET atomization [62, 93]. The feasibility of matrix-assisted laser desorption ionization (MALDI)D timeDof-Bight mass spectrometry (TOF-MS) prior to ES tandem MS as applied to tryptic protein digests has also been explored [135, 136]. 

Hop, C. E. C. A., and Bakhtiar, R. (1997). An introduction to electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry—essential tools in a modern biotechnology laboratory. Biospectroscopy 3, 259-280. 

On-probe purification using derivatized MALDI probe surfaces has been described to simplify the sample preparation process. Various developments in this field have allowed the introduction of new techniques such as the surface-enhanced laser desorption ionization (SELDI) [42], The surface of the probe plays an active role in binding the analyte by hydrophobic or electrostatic interactions, while contaminants are rinsed away. In the same way, this technique uses targets with covalently coupled antibodies directed against a protein, allowing its purification from biological samples as urine or plasma. Subsequent addition of a droplet of matrix solution allows MALDI analysis. 

A variety of MS formats are widely accepted and applied in the pharmaceutical industry. The specific MS application is often defined by the sample introduction technique. The pharmaceutical applications highlighted in this article feature two types of sample introduction techniques dynamic and static. Dynamic sample introduction involves the use of high-performance liquid chromatography (HPLC) on-line with MS. The resulting liquid chromatography/mass spectrometry (LC/MS) format provides unique and enabling capabilities for pharmaceutical analysis. The electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) modes are the most widely used. Static sample introduction techniques primarily use matrix-assisted laser desorption/ionization (MALDI). ... 

Until 1988, the mass spectrometric analysis of peptides and proteins was difficult. Some results were achieved using (continuous-flow) fast-atom bombardment (FAB) and Cf plasma desorption. The major breakthrough in the characterization of proteins by mass spectrometry (MS) is due to the introduction of matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) in 1988. Currently, peptides and proteins form the compound class most intensively studied by MS. This is primarily due to the prominent role ESI-MS and MALDI-MS play in the field of proteomics. 

Another important development in the field of biopolymer analysis is the introduction of matrix-assisted laser desorption ionization (MALDl), which is a rather recent soft ionization technique that produces molecular ions of large organic molecules. In combination with time-of-flight (TOP) mass spectrometry, it was proposed as a valuable tool for the detection and characterization of biopolymers, such as proteins, peptides, and oligosaccharides, in many types of samples.The use of these recently developed techniques has not decreased the use of chromatography in determinations of biopolymers. Some efforts on the adaptation of the separation abilities of HPLC to the high potential of MALDl-TOF for the sensitive determination of additives in biocomposites are currently being carried out. 

Recent advances in protein analysis by MS are due to the introduction of electrospray ionization (ESI), matrix-assisted laser desorption ionization (MALDI), MSN scan modes, as well as improvements in instrument sensitivity, resolution, and mass accuracy. With these improved techniques, researchers will continue to use MS to help elucidate primary, secondary, and to a lesser extent, tertiary structure of proteins. 

The analysis of proteins by mass spectrometry has emerged as the techifique of choice for obtaining high performance results from small amounts of analyte. Interest in this analytical technique has increased primarily as the result of the introduction of the electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) sources. These innovations permit nonvolatile molecules to be readily introduced into the gas phase. 

One of the most significant developments in mass spectrometry in the recent years is the introduction of a new class of ionization methods where samples in either solid or liquid state can be directly ionized in their native environment under ambient conditions (rather than inside a mass spectrometer) without any sample preparation. This new class of ionization methods is often referred to as ambient ionization methods [1,2], Because these methods generally ionize analytes on the surface or near the surface of the samples at atmospheric pressure, they have also been called atmospheric pressure surface sampling/ionization methods or direct/open air ionization methods [3], Since the first reports on ambient ionization with desorption electrospray ionization (DESI) [4] and direct analysis in real time (DART) [5], numerous reports have been published on the applications of these new ionization methods as well as the introduction of many related ambient ionization methods such as desorption atmospheric pressure chemical ionization (DAPCI) [6], atmospheric solid analysis probe (ASAP) [7], and electrospray-assisted laser desorption/ionization (ELDI) [8], Recently, two reviews of the various established and emerging ambient ionization methods have been published [2,3],... 

Mass spectrometry has been an established analytical technique in organic chemistry for many years. Until recently, however, the very low volatility of proteins made mass spectrometry useless for the investigation of these molecules. This difficulty has been circumvented by the introduction of techniques for effectively dispersing proteins and other macromolecules into the gas phase. These methods are called matrix-assisted laser desorption-ionization (MALDI) and electrospray spectrometry. We will focus on... 

Mass Spectrometric Detection. The very small volumetric flow rates of less than 1 pi,/min from electrophoresis capillaries make it feasible to couple the effluent directly to the Ionization source of a mass spectrometer. The most common sample-introduction and ionization interface for this purpose is currently electrospray (Section 20B-4), although fast atom bombardment, matrix-assisted laser desorption-ionization (MALDI) spectrometry, and inductively coupled plasma mass spectrometry (ICPMS) have also been used. Because the liquid sample must be vaporized before entering the mass spectrometry (MS) system. 

The introduction of Matrix-Assisted Laser Desorption/Ionization (MALDI) and Electrospray Ionization (ESI) (Chapter 1) has dramatically increased the mass range for molar mass analyses by mass spectrometry. In principle, both techniques are able to produce intact quasi-molecular ions of polymers with high molar mass (>100,000 Da). 

Figure 3.9 Schematics of the use of affinity protein microchips. Upper panel Sample introduction (A) and affinity binding (B) of proteins of interest. Lower panel Laser desorption/ionization (C) and MS interrogation (D).

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