Spectrometry vacuum system

The direct sampling of solutions is often necessary in a variety of situations such as biological fluids and eluants from liquid chromatography and capillary electrophoresis separation devices. Liquid solutions are difficult to handle by the mass spectrometry vacuum system and require some novel introduction and ionization systems. The last two decades have witnessed the development of some unique ionization methods that are suitable for direct analysis of sample solutions the important ones are discussed below. 

These pumps are ubiquitous in mass spectrometry vacuum systems the mode of operation is illustrated in Figure 6.37. It comprises a cylindrical cavity with entrance and exit ports used to draw in the gas to be... 

Interfacing of solution-based separation techniques with mass spectrometry has historically been a challenge because of the incompatibility of the used solvent with the vacuum system. Standard electron impact (El) ionization with techniques such as particle beam require samples to be vaporized under high vacuum for ion formation to occur. 

It has been the purpose of this paper to provide an overview of the basic differences and similarities of the various types of Instruments which detect Ionized particles emitted from surfaces by energetic particle bombardment. Since the scope of secondary ion mass spectrometry Is so broad, It is not surprising that no one Instrument has been designed to perform optimally for all types of SIMS analyses. Design aspects of the primary beam, extraction optics, mass spectrometer, detection equipment and vacuum system must be considered to construct an Instrument best suited for a particular purpose. 

The technique of laser desorption (LD) has been widely used in mass spectrometry (J, 2) to desorb and to ionize high molecular weight or other nonvolatile samples, most often using time-of-flight (3. 4 ) or Fourier transform ion cyclotron resonance (FTICR) ( 5. 6 ) mass spectrometers for mass analysis. In this technique, highly focussed laser irradiation, most often with a power density of at least 10° W/cm, is used to desorb and ionize a solid sample that has been inserted into the high vacuum system of the mass spectrometer. 

Ion mobility spectrometry (IMS) is an instrumental method where sample vapors are ionized and gaseous ions derived from a sample are characterized for speed of movement as a swarm in an electric field [1], The steps for both ion formation and ion characterization occur in most analytical mobility spectrometers at ambient pressure in a purified air atmosphere, and one attraction of this method is the simplicity of instrumentation without vacuum systems as found in mass spectrometers. Another attraction with this method is the chemical information gleaned from an IMS measurement including quantitative information, often with low limits of detection [2 1], and structural information or classification by chemical family [5,6], Much of the value with a mobility spectrometer is the selectivity of response that is associated with gas-phase chemical reactions in air at ambient pressure where substance can be preferentially ionized and detected while matrix interferences can be eliminated or suppressed. In 2004, over 20000 IMS-based analyzers such as those shown in Fig. 1 are placed at airports and other sensitive locations worldwide as commercially available instruments for the determination of explosives at trace concentration [7],... 

Samples sufficiently volatile for gas chromatography are readily handled by mass spectrometry. The two instruments are chiefly incompatible in the vast difference in operating pressures 760mmHg at the column exit and 10 -10" mm Hg in the analyser of the mass spectrometer. There are two solutions the vacuum system can be designed to accommodate a substantial fraction of the column effluent or a molecular separator can be employed to enrich sample relative to carrier gas effecting pressure reduction prior to transmission to the ion source. 

Another convenient way to classify ionization sources, rather than from the perspective of odd- or even-electron ion generation, is in relation to where the ions are created relative to the vacuum system that is, either generated at atmospheric pressure or in a vacuum. The two most common atmospheric pressure ionization sources, electrospray and atmospheric pressure chemical ionization, are arguably the most common ionization techniques applied in quantitative mass spectrometry today. However, discussion of earlier ionization sources is useful, as many of these techniques are still commonplace and their understanding provides a framework for appreciation of atmospheric pressure ionization technology and what it has to offer the pharmaceutical industry. 

The plasma sources developed for atomic emission spectrometry have also been shown to be very suitable ion sources for mass spectrometry. This is particularly true for electrical discharges at pressures in the 1-5 mbar range and sources at atmospheric pressure since the powerful vacuum systems became available, with which the pressure difference between the mass spectrometer (of the order of 10 s mbar) and the source can be bridged. 

The base pressure of the spectrometer system was 4x10 mbar and during the measurements 2-8x10 mbar. The purity of the vacuum system was steadily monitored by residual gas mass spectrometry (Quadrex 200, Leybold) to exclude artefacts. 

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