Electrospray ionization technique

Mass Spectrometry Mass to charge ratio (m/z) allows specific compound ID determination. Several t)rpes of ionization techniques electrospray, atmospheric pressure chemical ionization, electron impact. The detector usually contains low volume cell through which the mobile phase passes carrpng the sample components. 

The past years have seen the development of two important ionization techniques electrospray ionization (ESI) and matrix-assisted laser desorption (MALDI), which have been used especially in conjunction with quadrupole, time of flight (TOF) and ion cyclotron (IC) analyzers. Both ionization techniques have revolutionized the essence of mass spectrometry itself, radically increasing the upper mass limit and thus the applicability of the mass spectrometric technique and indirectly affecting the endeavors for improved resolution and sensitivity. With these techniques, the analysis of peptides, proteins and oligonucleotides has become possible. The aim of this chapter is to demonstrate the capabilities of these techniques, especially electrospray mass spectrometry in conjunction with HPLC techniques, for the analysis of combinatorially generated compounds and libraries, and to exemplify and discuss both the potentials and limits of these analytical techniques. 

Mass spectrometry currently has assumed a central role in protein sequencing. This development has been possible with the introduction of two highly sensitive ionization techniques electrospray ionization (ESI) and matrix-assisted laser desorption and ionization (MALDI) and the advent of improved instrumentation capable of high-mass and high-sensitivity detection. Currently, biopolymers with a molecular mass over 100,000 Da are analyzed routinely. In the past, fast atom bombardment (FAB) [6,7] and Cf plasma desorption (PD) ionization [8] also played a limited role in protein sequencing. Mass spectrometry now has assumed... 

See also Electrophoresis Overview Principles. Fluorescence Overview Instrumentation. Mass Spectrometry Overview Atmospheric Pressure Ionization Techniques Electrospray. 

See also Mass Spectrometry Overview Ionization Methods Overview Eiectron Impact and Chemical Ionization Atmospheric Pressure Ionization Techniques Electrospray Liquid Secondary Ion Mass Spectrometry Matrix-Assisted Laser Desorption/lonization Mass Separation Ion Traps Time-of-Flight. 

Being a very soft ionization technique, electrospray does not disrupt noncovalent bonds in complexes in solution. Complexes of an enzyme with a substrate, enzyme with inhibitor, and conglomerates of proteins can be detected by ESI. This development has led to the examination of protein-protein interactions by means of ESI MS. 

See also Mass Spectrometry Ionization Methods Overview Atmospheric Pressure Ionization Techniques Electrospray Matrix-Assisted Laser Desorption/lonization Time-of-Fiight. Proteins Traditionai Methods of Sequence Determination. Proteomics. 

Mass spectrometry This is often used for analysis of plastics. Thermal degradation can be carried out using an ion source, or in a pyrolyzer connected directly to a mass spectrometer or via a chromatographic column. Two soft ionization techniques, electrospray ionization and matrix-assisted laser desorption ionization (MALDI), are the most common in the analyses of large molecules. MALDI-MS is usually used offline but online connection with a... 

Leinonen, A. Kuuranne, T. Kostiainen, R. Liquid chromatography/mass spectrometry in anabolic steroid analysis—optimization and comparison of three ionization techniques Electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization. J. Mass Spectrom. 2002, 37 (7), 693-698. 

Among the different types of ionization techniques, electrospray ionization (ESI) is most frequently used in the analysis of tropane alkaloids. As easily protonated weak bases, the alkaloids are analyzed in positive mode. For this, 0.1 % formic acid or acetic acid is usually added to the mobile phase to enhance protonation and increase sensitivity. Only volatile buffers such as ammonium acetate can be used, as buffers such as phosphate may interfere with the ESI process. The latter is a soft ionization technique producing very little fragmentation, which provides information on the molecular mass of the compounds. 

The optimal condition is to use a HR instrument able to give an accurate MS/MS product ion spectrum in order to obtain the elemental composition of both precursor and product ions. In this section these analyzers will be taken into account, highlighting the strengths and weaknesses. However, due to the use of different atmospheric pressure ionization sources and consequently different optimal conditions, the comparison between distinct LC-MS systems could give a non realistic comparison between mass analyzers (Soler et al. 2005, 2006, 2007). Among the possible ionization techniques, electrospray (ESI) is by far the most widely used as compared with atmospheric-pressure chemical ionization (APCI) or the more recent atmospheric-pressure photoionization (APPI) (Krauss et al. 2010). 

ELSD), but in this case, careful calibratioD is required for quantification. A variety of MS detectors (quadrupole, ion trap, time-of-flight) using different ionization techniques (electrospray [ESI], atmospheric pressure chemical ionization [APCI]) have also been used for analyzing fatty acids (Lima and AbduUa, 2002). With suitable derivatives, detection by chemiluminescence (Ohba, Kuroda, and Nakashima, 2002) and under appropriate conditions electrochemical detection (Kotani, Kusu, and Takamura, 2002) are also possible. 

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