Component ionized

Fig. 2.15 Positive ion ESI mass spectra under flow injection conditions for a five-component mixture. (A) Mass spectrum for the direct anal)rsis of the mixture of which only two components ionize in the positive ion mode ethidium bromide (MW 314 Da) andWY311 (MW 319 Da). (B) Mass spectrum of the CPC spin column eluate for the mixture without RNA present. Neither...

Fig. 7A-D. SFC/ELSD/CLND/MS analysis of an equimolar mixture of Tolbutamide, Fmoc-Ile-OH, Mebendazole, and Prednisolone. The column flow rate was 5 ml/min. A portion of the column effluent was split to each of the three detectors (CLND, 200 pl/min ELSD,200 pl/min MS, 100 pl/min). A makeup flow of 50/50 MeOH/H20 (300 pl/min) was added to the flow stream diverted to the mass spectrometer ion source. Mass spectra were acquired using electrospray ionization with no special modifications to the ion source A total ion current chromatogram showing two of the four components ionize efficiently under electrospray ionization conditions B ELSD chromatogram of the four components, all showing comparable response C UV chromatogram (254 nm) shows some selectivity in detection as does D D CLND detection. Reprinted from [7] with permission from D.B. Kassel...

Mini/V. When eliminating V in terms of the mass of solution we sum over all component species s from which the final mixture was made up, while ignoring the fact that many of the components ionize in going into solution. Thus,... 

The choice of an ionization source must be consistent with the mass spectrometer inlet system, as described above, and the ionization characteristics of the analyte. Likewise, the appropriate choice of mass analyzer is highly application-, compound-, and matrix-dependent, and each mass analyzer requires certain characteristics from its ion detector The variety of individual ionization, mass analyzer, and ion detector systems that can be integrated creates a myriad of unique mass spectrometer systems, each with certain advantages and disadvantages. To add even more complexity to the situation, modular configuration of these individual components (ionization source, mass analyzer, and detector) is not limited... 

Adult men and women possess about 1300 g and 1000 g of calcium respectively, more than 99% of which is in bone and teeth. Although the absolute amount of calcium in the extracellular fluid is small, this fraction is stringently regulated. Normal serum calcium ranges from 8.5 to 10.4 mg/dL (4.25-5.2 mEq/L, 2.1-2.6 mM) and includes three components ionized (-50%), protein-bound (-40%, predominantly to albumin a decrease in albumin of 1.0 g/dL from the normal value of 4.0 g/dL typically decreases total serum calcium by -0.8 mg/dL), and complexed to anions such as phosphate and citrate (-10%) (Figure 61-1). 

Throughout its various applications, all MS is based on the measurement of the miz ratios of charged particles in a vacuum. In order to measure the miz ratio of samples, all mass spectrometers contain three main components ionization source, mass analyzer, and ion detector. 

Gas-phase appearance potentials for nucleotide bases were measured in early mass spectrometry experiments (8). In the first photoelectron (PE) probe of a nucleotide component, ionization potentials (IPs) of the valence manifold of ir and lone-pair orbitals of uracil were measured (9). This was followed by numerous photoelectron... 

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

Arnold F 1980 The middle atmosphere ionized component Vth ESA-PAG Symposium on European Rocket and Baiioon Programmes and Reiated Research (Bournemouth, UK ESA) pp 479-95... 

Ion-exchange methods are based essentially on a reversible exchange of ions between an external liquid phase and an ionic solid phase. The solid phase consists of a polymeric matrix, insoluble, but permeable, which contains fixed charge groups and mobile counter ions of opposite charge. These counter ions can be exchanged for other ions in the external liquid phase. Enrichment of one or several of the components is obtained if selective exchange forces are operative. The method is limited to substances at least partially in ionized form. 

For mixture.s the picture is different. Unless the mixture is to be examined by MS/MS methods, usually it will be necessary to separate it into its individual components. This separation is most often done by gas or liquid chromatography. In the latter, small quantities of emerging mixture components dissolved in elution solvent would be laborious to deal with if each component had to be first isolated by evaporation of solvent before its introduction into the mass spectrometer. In such circumstances, the direct introduction, removal of solvent, and ionization provided by electrospray is a boon and puts LC/MS on a level with GC/MS for mixture analysis. Further, GC is normally concerned with volatile, relatively low-molecular-weight compounds and is of little or no use for the many polar, water soluble, high-molecular-mass substances such as the peptides, proteins, carbohydrates, nucleotides, and similar substances found in biological systems. LC/MS with an electrospray interface is frequently used in biochemical research and medical analysis. 

In principle, DSI is the simplest method for sample introduction into a plasma torch since the sample is placed into the base of the flame, which then heats, evaporates, and ionizes the sample, all in one small region. Inherent sensitivity is high because the sample components are already in the flame. A diagrammatic representation of a DSI assembly is shown in Figure 17.4. 

As described above, the mobile phase carrying mixture components along a gas chromatographic column is a gas, usually nitrogen or helium. This gas flows at or near atmospheric pressure at a rate generally about 0,5 to 3.0 ml/min and evenmally flows out of the end of the capillary column into the ion source of the mass spectrometer. The ion sources in GC/MS systems normally operate at about 10 mbar for electron ionization to about 10 mbar for chemical ionization. This large pressure... 

As each mixture component elutes and appears in the ion source, it is normally ionized either by an electron beam (see Chapter 3, Electron Ionization ) or by a reagent gas (see Chapter I, Chemical Ionization ), and the resulting ions are analyzed by the mass spectrometer to give a mass spectmm (Figure 36.4). 

In the earliest interface, a continuous moving belt (loop) was used onto which the liquid emerging from the chromatographic column was placed as a succession of drops. As the belt moved along, the drops were heated at a low temperature to evaporate the solvent and leave behind any mixture components. Finally, the dried components were carried into the ion source, where they were heated strongly to volatilize them, after which they were ionized. 

It is worth noting that some of these methods are both an inlet system to the mass spectrometer and an ion source at the same time and are not used with conventional ion sources. Thus, with electrospray, the process of removing the liquid phase from the column eluant also produces ions of any emerging mixture components, and these are passed straight to the mass spectrometer analyzer no separate ion source is needed. The particle beam method is different in that the liquid phase is removed, and any residual mixture components are passed into a conventional ion source (often electron ionization). 

By allowing any solution, but particularly the eluant from a liquid chromatographic column, to flow continuously (dynamically) across a target area under bombardment from fast atoms or ions (FAB or FIB), any eluted components of a mixture are ionized and ejected from the surface. The resulting ions are detected and recorded by a mass spectrometer. The technique is called dynamic FAB or dynamic LSIMS. 

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