Mass 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... 

Few of the naturally occurring elements have significant amounts of radioactive isotopes, but there are many artificially produced radioactive species. Mass spectrometry can measure both radioactive and nonradioactive isotope ratios, but there are health and safety issues for the radioactive ones. However, modem isotope instmments are becoming so sensitive that only very small amounts of sample are needed. Where radioactive isotopes are a serious issue, the radioactive hazards can be minimized by using special inlet systems and ion pumps in place of rotary pumps for maintaining a vacuum. For example, mass spectrometry is now used in the analysis of Pu/ Pu ratios. 

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. 

Three basic techniques, and variations thereof, have been used in recent years to study aspects of gas-phase ion-molecule reactions pertinent to organic systems they are ion cyclotron resonance spectrometry, flowing afterglow, and high pressure mass spectrometry. The essential feature of these techniques is that ions produced under vacuum are allowed to undergo from few to many collisions with neutrals before they are neutralized at the walls of the instrument. 

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