Electrospray stable

See also Atomic Mass Spectrometry Inductively Coupled Plasma. Gas Chromatography Mass Spectrometry. Liquid Chromatography Liquid Chromatography-Mass Spectrometry. Mass Spectrometry Ionization Methods Overview Electrospray Stable Isotope Ratio. 

Ions formed in an electrospray or similar ion source are said to be thermolized, which is to say that their distribution of internal energies is close to that expected for their normal room-temperature ground state. Such ions have little or no excess of internal energy and exhibit no tendency to fragment. This characteristic is an enormous advantage for obtaining molecular mass information from the stable molecular ions, although there is a lack of structural information. 

The pump must provide stable flow rates from between 10 ttlmin and 2 mlmin with the LC-MS requirement dependent upon the interface being used and the diameter of the HPLC column. For example, the electrospray interface, when used with a microbore HPLC column, operates at the bottom end of this range, while with a conventional 4.6 mm column such an interface usually operates towards the top end of the range, as does the atmospheric-pressure chemical ionization (APCI) interface. The flow rate requirements of the different interfaces are discussed in the appropriate section of Chapter 4. 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

Electrospray ionization will often produce ions that are fully coordinated, stable, and nonreactive in the gas phase. These ions may be probed by removal of ligands to form coordinatively unsaturated ions that are generally reactive. The chemical activity of metal cluster ions differs markedly and often shows size specific enhanced reactivity or lack of reactivity. Silver cluster ions Ag are fairly inert similar to Ag+. Platinum cluster ions PL are quite reactive similar to Pt+. Often, large cluster ions only appear to react with one donor molecule such as benzene this may be due to low concentrations of reactants or short reaction times. Similar clusters may react with a larger number of smaller molecules, and so until more information is available, rules for the coordination behavior of metal clusters are as yet not available. 

Lately, electrospray ionisation technique (ESI-MS) which is compatible with RP-HPLC has been routinely used. This allows labile molecules to be studied intact. Sample molecules are simultaneously nebulised and ionised at atmospheric pressure in the presence of several thousand volts. The resulting ions can be multi-protonated (multiply charged) and relatively stable. This mode of ionisation has recently been used in the development of RP-HPLC coupled with positive ion ESI-MS and ion-trap MS protocols for the identification and... 

Very low flow electrospray is called nanoelectrospray [26] where the samples are infused into the mass spectrometer at the nanoliter flow rate range. The infusion of a few microliters will result in a stable signal for more then 30 min, using pulled capillaries or chip-based emitters [27]. With infusion, signal averaging allows to improve the limit of detection in tandem mass spectrometry. Nanoelectrospray is particularly important in combination with nanoflow liquid chromatography or chip-based infusion for the analysis of peptides and proteins. 

Liang, H.R. Foltz, R.L. Meng, M. Bennett, P. Ionization enhancement in atmospheric pressure chemical ionization and suppression in electrospray ionization between target drugs and stable-isotope-labeled internal standards in quantitative liquid chromatography/tandem mass spectrometry. Rapid Commun. Mass Spectrom. 2003, 17, 2815—2821. 

The development of electrospray ionization (ESI) enabled multiply charged ions, solvated ions, and metal-coordinated species to be formed in the gas phase. Recently, Kass and coworkers showed that collision-induced dissociation (CID) of RC02Li containing ions (e.g. 1) leads to the loss of carbon dioxide and the attachment of Li to R (Scheme 1) . This is an exceptionally stable alkyl lithium compound that could be synthesized, in the gas phase, under relatively mild conditions. 

Further information regarding the composition of mixed micelles can be obtained by coupling to mass spectrometry. However, the use of surfactants in electrospray ionization will always be fraught with difficulties because contamination of the interface with nonvolatile tensides causes undesirable effects. Stable mixed micelles can be measured only by employing nonequilibrium conditions (only buffers without micellar components). Two further variants of MEKC-MS have been developed and successfully used in recent years, but these are not readily employed for the electrophoretic characterization of micelles, since either a partial filling technique or surfactants of high molecular mass have to be used (37). 

Provide makeup flow to get stable electrospray conditions (2-5 /xL/ min)... 

Following extractive deproteinization of the plasma, the amino acids (and their stable-isotope-labeled internal standards) are separated by HPLC and introduced into the mass spectrometer. Electrospray ionization results in the formation of electrically charged molecules, which are separated on the basis of their mass/charge (m/z) ratio in the first quadrupole. Following fragmentation in the collision cell, the characteristic fragment for each amino acid is selected in the second quadrupole. This process is named multiple reaction monitoring. 

As described in 2.2.3.1, Principles of Assay , tHcy must be produced by chemical reduction, which is achieved in the method described here by dithiothreitol. tHcy is analysed by HPLC separation followed by electrospray ionisation and then separation of the ionised molecule in the first mass spectrometer, then fragmentation into a specific ion fragment in the second. Quantification is based on comparison of the signal from natural Hey (transition m/z 135.9 —< m/z 89.9) with that of the stable isotope internal standard (transition m/z 139.9 —< m/z 93.9). 

AdoMet and AdoHcy are separated by HPLC and analysed by electrospray ionisation-tandem mass spectrometry. Quantification is based on comparison of the signal from natural AdoMet (transition m/z 399 ->- m/z 250) and AdoHcy (transition m/z 385 ->- m/z 135 and 134) with that from analogous transitions of the stable isotope internal standards. 

Gellekink H, van Oppenraaij-Emmerzaal D, van Rooij A, Struys EA, den Heijer M, Blom HJ (2005) Stable-isotope dilution liquid chromatography-electrospray injection tandem mass spectrometry method for fast, selective measurement of S-adenosylmethionine and S-adeno-sylhomocysteine in plasma. Clin Chem 51 1487-1492... 

Magera MJ, Helgeson JK, Matern D, Rinaldo P (2000) Methylmalonic acid measured in plasma and urine by stable-isotope dilution and electrospray tandem mass spectrometry. Clin Chem 46 1804-1810... 

Young SP, Stevens RD, An Y, Chen YT, Millington DS (2003) Analysis of a glucose tetrasac-charide elevated in Pompe disease by stable isotope dilution-electrospray ionisation tandem mass spectrometry. Anal Biochem 316 175-180... 

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