Atmospheric pressure matrix-assisted laser applications

API offers unique opportunities for the implementation of new sources or to develop new applications. Atmospheric pressure matrix assisted laser desorption (AP-MALDI) [21] can be mounted on instruments such as ion traps which were originally designed only for electrospray and LC-MS. New API desorption techniques such as desorption electrospray (DESI) [22] or direct analysis in real time (DART) [23] have been described and offer unique opportunities for the analysis of surfaces or of solid samples. 

Pihlainen, K., Grigoras, K., Franssila, S., Ketola, R., Kotiaho, T., and Kostiainen, R. (2005). Analysis of amphetamines and fentanyls by atmospheric pressure desorption/ionization on silicon mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry and its application to forensic analysis of drug seizures. J. Mass Spectrom. 40 539-545. 

Strege summarized the technique of high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) in dereplication of natural products. In contrast to earlier electron impact ionization (El), ESI technique is applicable to virtually any ion in solution with a soft ionization process. A comparison of ESI with fast atom bombardment (FAB), matrix assisted laser desorption ionization (MALDI), atmospheric pressure chemical ionization (APCI) and other techniques demonstrates its superior sensitivity, compatibility and reliability when coupled with HPLC [51]. 

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). ... 

See also Carbohydrates Overview. Elemental Speciation Overview. Food and Nutritional Analysis Overview. Gas Chromatography Mass Spectrometry. Lipids Overview. Liquid Chromatography Liquid Chromatography-Mass Spectrometry Food Applications. Mass Spectrometry Overview Principles Ionization Methods Overview Atmospheric Pressure Ionization Techniques Eiectrospray Matrix-Assisted Laser Desorption/lonization Pyrolysis. Proteins Traditional Methods of Sequence Determination. Vitamins Overview. 

The successful on-line interfacing of several ion sources has made them dominant players in quantitative analyses using mass spectrometry. These include electron ionization (El) and chemical ionization (Cl) both coupled to GC, and the atmospheric pressure ionization (API) methods of atmospheric pressure chemical ionization (APCI) atmospheric pressure photoionization (APPI), and electrospray ionization (ESI) coupled to LC. In addition, matrix assisted laser desorption ionization (MALDI) is seeing increased application in off-line LC/MS applications. 

In recent years, TLC was successfully combined with different ionization techniques, matrix-assisted laser desorption/ionization (MALDI), ESI, atmospheric pressure chemical ionization (APCI), desorption electrospray ionization (DESI), electrospray-assisted laser desorption ionization (ELDI), and LDI for identification and quantification of organic and biomolecules. In this section, the interfacing of TLC techniques with MALDI-ESI/MS, DESI-MS, ELSI-MS, and LDI-MS will be described, performance will be discussed, and selected applications in the separation and identification of lipids, gangliosides, dyes, drugs, and medicinal compounds will be presented. 

To perform MS, one must make ions from neutral molecules. Ionization methods have advanced from the classic electron ionization (El), through chemical ionization (CI), field desorption (FD), fast atom bombardment (FAB) and thermospray to the atmospheric pressure ionization (API) techniques currently favored. El is classic, but is restricted in its applicability to thermally stable, volatilizable compounds. ED was always a specialized niche technique applicable to some larger compounds. EAB enjoyed a meteoric rise and fall in use first reported in 1981, but has all but disappeared now, being replaced by the API techniques atmospheric pressure Cl (APCI) °° and electrospray ionization (ESI). ° Matrix-assisted laser desorption ionization (MALDI) has shown significant utility for characterizing larger proteins, approximately 100 kDa and larger. 

Numerous ionization techniques have been reported in the last century, which are applicable to modern mass spectrometry. Depending on the method of analyte introduction (e.g., direct inlet, GC, LC, or capillary electrophoresis different strategies have been employed including El, Cl, thermospray, particle beam, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI), etc. In sports drug testing, only selected approaches have been applied to routine doping control analyses, which are outlined in the following. 

MS is undoubtedly the solution of the near future for LC detection. Improvements made to interfacing devices together with a continuous and sensible diminution of instrumentation costs promote MS as a universal/selective tunable detection system. Atmospheric pressrue electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the most robust and popular devices for interfacing MS to LC systems. In Table 9, LC-MS data for some pesticides are given. Although ESI and APCI are more often used, other LC-MS interfaces produce reliable results in pesticide applications thermospray (TSI), particle beam (PBI) and matrix-assisted postsource decay laser desorption/ionization (CID-PSD-MALDI). 

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