Ionization external

More direct observations of the kinetic energy dependence of cross-sections should be possible using external ionization techniques where the reactant ion can be chosen by initial mass analysis and, in principle, its energy more readily controlled. Several studies using external ionization techniques, both with (2, 10, 45) and without (20, 21, 27, 41) preliminary mass selection of the reactant ion, have been reported. However, apparently with these techniques it is not possible to obtain well-defined primary ion beams at energies below 0.5-1 e.v. a region of critical importance both experimentally and theoretically. 

Because of these limitations to both the conventional internal ionization and external ionization techniques it has been impossible to obtain accurate kinetic data for the reactions of thermal energy ions. Such thermal energy data are desirable for applications in such areas as radiation chemistry, discharge and combustion phenomena, and upper atmosphere research. 

The resonating positive charge in Dobner s violet is formed not by internal ionization but rather by external ionization. Other colored cations of this general type are numerous the cation of acridine yellow, for example, can be ascribed the structure... 

E. C. Homing, M. G. Homing, D. I. Carroll, I. Dzidic, and R. N. Stillwell. New Picogram Detection System Based on a Mass Spectrometer with an External Ionization Source at Atmospheric Pressure. Anal. Chem., 45(1973) 936-943. 

As noted earlier, the development of the dual cell (37), tandem quadrupole-FTMS (46, 47) and external ionization cell (48, 49) has facilitated the coupling of FTMS and chromatographic methods. Advances in interfacing separation techniques with FTMS will be important in the analysis of mixtures, especially where high mass resolution is required. For example, liquid chromatographic introduction of mixtures isolated from biological systems directly into an FTMS for analysis would eliminate the need for laborious sample clean up. 

Figure 10 shows a schematic drawing of the ion transfer mechanism in the CMS 47 with external ionization. Figure 11a... 

With the successful implementation of differentially-pumped external ion sources, FTMS is rapidly becoming a routine mass spectrometric technique. Medium-pressure interfaces for the coupling of GC, LC, FAB, and liquid SIMS into the external ionizer are currently under development, and should become available in the near future. 

Recently, new 2D-methods for the analysis of complex mixtures have been developed for time-of-flight mass spectrometry (22), which could also be utilized in external ionization FTMS. Specifically, the combination of IR-laser desorption of nonvolatile neutrals, followed by adiabatic cooling to 2°K in a supersonic jet, and subsequent compound-selective Resonance-Enhanced Multiphoton Ionization (REMPI) could increase the role of FTMS in the analysis of biological mixtures. The coupling of supersonic jets to the external ion source would also be of interest in ion- and neutral cluster experiments. 

The rate constant kQ has to be distinguished from the rate constant of external ionization, kef, called in this review rate constant of propagation of the macroester (see p. 81) (thus, the meanings of kei and kp are the same) and related to reaction (113) ... 

Cattaneo M, Canciani MT, Matmued PM Human platelet aggregation and rdease reaction induced by platelet activating factor (PAF-aoedier)-effects of acetylsalicylic add and external ionized caldum. Thromb Haemostas 1985 221-224... 

Figure 2.3 Ion-trap mass spectrometer with external ionization source.

Methanol and acetonitrile are most widely used as organic modifier (reversed-phase LC). For most compounds, a high water content is favourable in the TSP buffer ionization mode. At modifier contents exceeding 50% modifier, external ionization, i.e., filament-on or discharge-on, must be applied. The typical flow-rates are in the range of 1.0 to 1.5 ml/min. 

Exposure to natural sources of external ionizing radiation results from the levels of cosmic and terrestrial X and gamma radiation present in the environment. Cosmic radiation at the earth s surface is affected by altitude, geomagnetic latitude, and solar modulation. For example, the dose rate at... 

The optimal HPLC separation conditions for the nemadectins precluded the use of "buffer only" ionization. The Finnigan TSP-46 thermospray source is equipped with a filament and a discharge electrode as choices for an external ionization method. Both positive and negative ion detection are available. The best choice for an ionization method and for the mode of ion detection would have to provide adequate sensitivity for minor component analysis, unambiguous molecular weight information, and sufficient fragmentation to differentiate between components with similar retention times and identical molecular weights. 

The second problem is that ion-ion or ion-neutral reactions can occur. Reactions (e.g., proton transfer) result in high abundance of protonated molecular ions in the mass spectrum. Thus QIT can be disadvantageous for determining chemical composition in manual spectral interpretation, because the presence of the (M + l)" ion tends to confuse the interpretation. Library spectral matching, however, is not affected if the spectral matching algorithm reflects the unique features of the QIT spectrum. An external ionization source with ion injection into the QIT is an alternative solution, because only ions are present in the trap (i.e., neutral analyte molecules that could participate in ion-molecule reactions are not present). The Thermo Finnigan PolarisQ GC/MS is an example of such an instrument. 

Like the QIT, ionization in the FT-ICR maybe performed either internally or externally to the cell. For several reasons, external ionization has become the technique of choice. External ionization allows the use of virtually any ionization method, and commercially available instruments are typically designed as general purpose instruments incorporating interchangeable ion sources. All three major suppliers of FT-ICR instruments (lonSpec, Bruker Daltonics, and Finnigan) offer external sources. 

Horning EC, Horning MG, Carroll DI, Dzidic I, Stillwell RN. New picogram detection system based on a mass spectrometer with an external ionization source at atmospheric pressure. Anal Chem 1973 45 936-43. 

Quadrupole ion trap mass analyzers merge the trapping characteristics of the ICR with the physical principles of the linear quadrupole mass analyzer. Quadrupole ion traps produce time-dependent spectra with excellent sensitivity and tandem mass spectrometry capabilities, but unlike the ICR they provide these ion trapping characteristics with physically smaller and considerably less expensive instrumentation, giving them a reputation as a powerful and accessible tool for both qualitative and quantitative mass spectrometry [43-47]. The capability of quadrupole ion traps to be configured with either internal and external ionization sources has expanded their utility for modem analytical applications [48—52]. 

Assessment of historical exposures at the Portsmouth Naval Shipyard for a study of lung cancer risk from external ionizing radiation... 

The external ionization involves addition of the monomer molecule to the covalent active species and, thus, means the covalent propagation. 

Horning and co-workers used the so-called atmospheric pressure ionization (API). The ions are formed at atmospheric pressure outside the mass spectrometer. After dV detection, the eluate from a chromatographic column (flow-rate of liquid 0.5 ml/min) is mixed with hot carrier gas (nitrogen) to aid evaporation at 300 C (Fig. 7). The entire effluent stream is vaporized and directed through the external ionization source of the API mass spectrometer. 

Ionization of the sample can take place outside of the ion storage area of the ion trap such external ionization is required for LC-MS using an ion trap and may be used for GC-MS. Alternatively, ionization can take place inside the ion storage area this internal ionization approach can be used for GC-MS. Inert gas may be introduced into the trap after initial ionization for MS-MS experiments using collision-induced dissociation. 

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