Desorption chemical ionisation

Desorption chemical ionisation (DCI) Fourier transform (FTMS) MicroChannel plate... 

Cl and El are both limited to materials that can be transferred to the ion source of a mass spectrometer without significant degradation prior to ionisation. This is accomplished either directly in the high vacuum of the mass spectrometer, or with heating of the material in the high vacuum. Sample introduction into the Cl source thus may take place by a direct insertion probe (including those of the desorption chemical ionisation type) for solid samples a GC interface for reasonably volatile samples in solution a reference inlet for calibration materials or a particle-beam interface for more polar organic molecules. This is not unlike the options for El operation. 

Applications Desorption chemical ionisation has proven potential in the analysis of thermally labile, nonvolatile and polar compounds [40,67,68], for the identification of unknown polymers and the study of the thermal degradation mechanisms of polymers. Considering the overall ease of DCI operation, the capability of analysing nonvolatile compounds, and the selectivity provided by choosing different reagent gases, DCI has found surprisingly few practitioners in the analysis of polymer additives. 

Desorption chemical ionisation (DCI) mass spectrometry has been used for detecting additives extracted from polymers [51,52] by a solvent as volatile as possible. To use the DCI probe, 1 -2 iL of the sample, in solution, are applied to the probe tip, composed of a small platinum coil, and after the solvent has been allowed to evaporate at room temperature, the probe is inserted into the source. The sample is then subject to fast temperature ramping. DCI does not seem to be the most suitable mass-spectrometric method for analysis of dissolved polymer/additive matrices, because ... 

DCI (1) Direct chemical ionisation (2) Desorption chemical ionisation... 

The nature of refractory methylarsenic compounds in estuary waters has been examined by desorption chemical ionisation mass spectrometry, and mass spectrometry [18]. 

In off-line coupling of LC and MS for the analysis of surfactants in water samples, the suitability of desorption techniques such as Fast Atom Bombardment (FAB) and Desorption Chemical Ionisation was well established early on. In rapid succession, new interfaces like Atmospheric Pressure Chemical Ionisation (APCI) and Electrospray Ionisation (ESI) were applied successfully to solve a large number of analytical problems with these substance classes. In order to perform structure analysis on the metabolites and to improve sensitivity for the detection of the various surfactants and their metabolites in the environment, the use of various MS-MS techniques has also proven very useful, if not necessary, and in some cases even high-resolution MS is required. 

Whilst on-line desorption chemical ionisation mass spectrometry (MS) has been used to analyse fermentation biosuspensions for flavones [11], the majority of MS applications during fermentations have been for the analysis of gases and volatiles produced over the reactor [12-15], or by employing a membrane inlet probe for volatile compounds dissolved in the biosuspensions [16-22]. It is obvious that more worthwhile information would be gained by measuring the non-volatile components of fermentation biosuspensions, particularly when the product itself is non-volatile, which is usually the case. 

Amoxicillin trihydrate did not give a useful mass spectrum by the conventional electron impact ionisation technique, even with a specialised in beam procedure which gave spectra from several other penicillins [26], Laser desorption [27] and desorption chemical ionisation [28] both gave pseudomolecular ions and the latter technique also gave significant fragmentation. 

Mares, P., Rezanka, T. and Novak, M. (1991) Analysis of human blood plasma triacylglycerols using capillary gas chromatography, silver ion thin-layer chromatographic fractionation and desorption chemical ionisation mass spectrometry. J. Chromatogr., 542, 145-59. 

Spanos, G. A., Schwartz, S. J., van Breemen, R. B. and Huang, C.-H. (1995) High performance liquid chromatography with light scattering detection and desorption chemical ionisation tandem mass spectrometry of milk fat triacylglycerols. Lipids, 30, 85-90. 

Juo and co-workers [94] have demonstrated that ammonia desorption chemical ionisation was a better ionisation technique than fast atom bombardment (FAB) for the determination of additives in PE extracts. 

In this procedure the unknown polymer was pyrolysed within the ion source of a mass spectrometer by a coiled filament designed for desorption chemical ionisation/desorption electron ionisation applications. Pyrolysis products ionised by 70 eV electron impact yielded highly reproducible mass spectra which were characteristic of the polymer. 

Vincenti and co-workers [241] used desorption chemical ionisation mass spectrometry to determine MWD in PS, PEG, polysiloxanes, and polynorbornene. 

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