Miniaturized vacuum pump

Nor is this all. Vitamin C is also taken up by white blood cells. When we are infected with bacteria, white blood cells called neutrophils mount the first defence. In the course of this defence, neutrophils vacuum up vitamin C from their surroundings, using miniature protein pumps in their membranes. The level of vitamin C inside the neutrophils increases tenfold within minutes, and if the infection persists, may reach 30 times the level of resting neutrophils, or 100 times that in plasma, even in someone taking massive oral supplements. 

While significant advances have been made toward the miniaturization and ruggedization of mass analyzers for space flight applications, considerably less attention has been given to the vacuum systems required to enable in situ MS. For this reason, the vacuum pumps often severely limit the overall capabilities of the mass analyzers they support. Specifically, in many applications commercially available vacuum pumps are too bulky, require too much power for spacecraft power sources, or are intolerant to the vibration and shock associated with space flight. 

Depending on the efficiency of the high vacuum pump, one major modification of the P T method may be necessary to keep the pressure in the ion source within acceptable limits. The optima] gas flow into the mass spectrometer is usually l-2mL/min, which means that a miniaturized P T system with a microtrap and a narrow-bore GC column is needed. Techniques for measuring halocarbons in the atmosphere by mass spectrometry have been used for several years (e.g., O Doherty et al., 1993), whereas systems for seawater measurements were developed more recently. Either a constant flow of seawater equilibrates with a gas which is subsampled for analysis (7. Butler, personal communication), or a modified P T system is used which allows for a larger range of halocarbons to be determined (Ekdahl and Abrahamsson, 1997). 

They do not require the use of additional carrier gases, vacuum pumps, or specialized power supphes. Most field-portable instruments use a weak radioactive ionization source to provide the ionization energy. These features significantly simplify the instrumentation and permit detector miniaturization for field operations. This technique has received a great deal of attention and its application is being rapidly expanded. 

A miniature cylindrical ion trap mass spectrometer with APCI and ESI capabilities was developed [22], The system includes a three-stage, differentially pumped vacuum system and can be interfaced to many types of atmospheric pressure ionization sources. 

The drawback of this approach turned out to be samples of submicrolitre level, which necessitated the development of a dedicated small measuring device with a very low dead volume. A portable lightweight apparatus, consisting in a miniaturized flow-through biosensor connected to a microdialysis probe at one side, and to a semi-vacuum pulse-free pump at the other was then built. A portable potentiostat equipped for data collection and storage was used to handle data. 

In order to avoid the loss of analyte, either as much of the LC effluent as possible has to be introduced into the mass spectrometer, or efficient analyte enrichment must be achieved in the LC-MS interface. Without modification, only 50nls of liquid can be introduced into a differentially pumped MS vacuiun system. Possible solutions to this flow-rate incompatibility problem are enlargement of the pumping capacity of the MS vacuum system, removal of solvent prior to the introduction of the analytes into the high-vacuum region, splitting away part of the effluent at the cost of analyte loss, and miniaturization of the internal diameter of the LC column. The currently applied interface, based on atmospheric-pressure ionization (API), is discussed in more detail below. 

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