And electrospray ionization

A connnon feature of all mass spectrometers is the need to generate ions. Over the years a variety of ion sources have been developed. The physical chemistry and chemical physics communities have generally worked on gaseous and/or relatively volatile samples and thus have relied extensively on the two traditional ionization methods, electron ionization (El) and photoionization (PI). Other ionization sources, developed principally for analytical work, have recently started to be used in physical chemistry research. These include fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ES). 

The advent of atmospheric-pressure ionization (API) provided a method of ionizing labile and nonvolatile substances so that they could be examined by mass spectrometry. API has become strongly linked to HPLC as a basis for ionizing the eluant on its way into the mass spectrometer, although it is also used as a stand-alone inlet for introduction of samples. API is important in thermospray, plasmaspray, and electrospray ionization (see Chapters 8 and 11). 

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

Atmospheric-pressure chemical ionization (APCI) and electrospray ionization are both soft ionization techniques which give rise, almost exclusively, to the production of molecular species. Structural information. 

When low -molecular-weight compounds are involved, both APCl and electrospray ionization are potentially of value and the first task is to decide which of these will give the more useful data. 

A method has been reported for the quantification of five fungicides (shown in Figure 5.39) used to control post-harvest decay in citrus fruits to ensure that unacceptable levels of these are not present in fruit entering the food chain [26]. A survey of the literature showed that previously [27] APCl and electrospray ionization (ESI) had been compared for the analysis of ten pesticides, including two of the five of interest, i.e. carbendazim and thiabendazole, and since it was found that APCl was more sensitive for some of these and had direct flow rate compatibility with the HPLC system being used, APCl was chosen as the basis for method development. 

Paganga, G. et al.. The polyphenolic content of fruit and vegetables and their antioxidant activities what does a serving constitute Free Radical Res., 30, 153, 1999. Maatta, K.R. et al.. High-performance liquid chromatography (HPLC) analysis of phenolic compounds in berries with diode array and electrospray ionization mass spectrometric (MS) detection Rihes species, J. Agric. Food Chem., 51, 6736, 2003. 

The most recent progress in MS analysis of chlorophylls has been obtained with the development of atmospheric ionization methods such as atmospheric pressure chemical ionization (APCl) and electrospray ionization (ESI). These techniques have demonstrated much more sensitivity than thermospray ionization, detecting chloro-... 

Notes Peptide fragments detected using MALDI and electrospray ionization (ESI)-MS. For more detail, please see Reference 33. 

N. Gamier, C. Cren Olive, C. Rolando, M. Regert, Characterization of the archaeological beeswax by electron ionization and electrospray ionization mass spectrometry, Analytical Chemistry, 74, 4868 4877 (2002). 

For the last several years, mass spectrometry with atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) have determined the trends in the analysis of dyes. Since 1987, various variants of ESI have been used in which droplet formation was assisted by compressed air,[1,2] temperature (e.g. Turbo Ion Spray ) or ultrasound, and they were able to handle flow rates up to 1 2 ml min This made a combination of analytical RPLC and ESI easily and widely used. The reason why it often was (and is) used instead of a traditional UV-Vis detector is the better sensitivity and selectivity of MS in comparison with spectrophotometric detection. Apart from these advantages, MS offers easily interpretable structural information. However, various... 

Mass spectrometry requires that the material being studied be converted into a vapor. Great strides have been taken in recent years to address this problem, especially in enticing large, thermally fragile (bio)molecules into the vapor state. Matrix assisted laser ionization-desorption (MALDI) and electrospray ionization (ESI) are two current forefront methods that accomplish this task. Even components of bacteria and intact viruses are being examined with these approaches. John B. Fenn and Koichi Tanaka shared in the award of a Nobel Prize in 2002 for their respective contributions to development of electrospray ionization and soft laser desorption. 

More recently, the El and electrospray ionization (ESI) mass spectra of 2,5-diaryl- and 2-arylamino-5-aryl-l,3,4-oxadiazoles, as well as their complexes with copper cations, were studied. Under ESI conditions, loss of NH3 and HNCO, from complexes of 2,5-diphenyl-l,3,4-oxadiazole, 2,5-bis(2-pyridyl)-l,3,4-oxadiazole, or 2,5-bis(4-pyridyl)-1,3,4-oxadiazole with copper cation, was observed <2004JMP272>. An unusual elimination of isocyanic acid was found in fragmentation of some protonated 2,5-diaryl derivatives <2002RCM390>. 

In 1988-1989, two processes were discovered that allowed the transfer of large molecules into the gas phase matrix-assisted laser desorption and ionization (MALDI) and electrospray ionization (Karas and Hillenkamp, 1988 Fenn et al., 1989). 

C.W. Huck, M.R. Buchmeiser and G.K. Bonn, Fast analysis of flavonoids in plant extracts by liquid chromatography-ultraviolet absorbance detection on poly(carboxylic acid)coated silica and electrospray ionization tandem mass spectrometric detection. J. Chromatogr.A 943 (2002) 33-38. 

Breindahl T, Andreasen K. 1999. Determination of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid in urine using high-performance liquid chromatography and electrospray ionization mass spectrometry. J Chromatogr B Biomed Sci Appl 732 155. 

Zamfir A, Seidler DC, Kresse H, Peter-Katalinic J. 2002. Structural characterization of chondroitin/dermatin sulfate oligosaccharides from bovine aorta by capillary electrophoresis and electrospray ionization quadrupole time-of-flight tandem mass spectrometry. Rapid Commun Mass Spectrom 16 2015. 

LC-NMR can be used to identify natural products in crnde plant extracts that usually consist of complex mixtnres. The crnde natural product extracts normally contain a great nnmber of closely related and difficult-to-separate compounds. The classical separation approach may become very tedious and time-consuming. The directly conpled HPLC-NMR presents an efficient separation techniqne together with a powerfnl spectroscopic method to speed up the identification process. LC-NMR has been nsed extensively for characterization of natnral prodncts. More recently, the combination of LC-NMR and LC-MS has been further developed in this field. Eor example, Wilson et al. have nsed combined on-flow NMR and electrospray ionization MS to characterize ecdysteroids in extracts of silene otites. After reversed-phase HPLC nsing D2O in acetonitrile-dj and UV detection, the LC flow was split 95 5 for the simnl-taneous detection by NMR and MS. The peaks of interest were analyzed by stop-flow NMR to give better quality spectra for structural assignment. 

Nilsson, S. L., Andersson, G., Sjoeberg, P. J. R., Bylund, D., Petersson, P., Joernten-Karlsson, M., and Markides, K. E. (2003). Phosphate buffers in capillary electrophoresis/mass spectrometry using atmospheric pressure photoionization and electrospray ionization. Rapid Commun. Mass Spectrom. 17, 2267-2272. 

Petty, I., Wisniewski, J.R., and Szewczuk, Z. (2001) Conformational stability of six truncated cHMGla proteins studied in their mixture by H/D exchange and electrospray ionization mass spectrometry. Acta Biochim. Pol. 48, 1131-1136. 

Lee KC, Cheuk MW, Chan W, Lee AW, Zhao ZZ, Jiang ZH, Cai Z (2006) Determination of glucosinolates in traditional Chinese herbs by high-performance liquid chromatography and electrospray ionization mass spectrometry. Anal Bioanal Chem 386 2225-2232... 

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