Working under Vacuum

All mass spectrometers work under vacuum conditions, that is, under a pressure inferior to atmospheric pressure, generally ranging from 10 to 10 torr (primary vacuum). A secondary vacuum is characterized by pressures from 10 to 10 torr. The quality of the vacuum is a determining factor for all analyses. 

The process consists of evacuating the carrier gas arriving in the source of the spectrometer and the residual atmospheric molecules such as nitrogen, oxygen, carbon dioxide, water, and eluted molecules from the chromatograph that have not been ionized and may contribute to pollution of the mass spectrometer. Another goal is to ensure correct functioning of the filament and the electron multiplier of the mass spectrometer that may be weakened by excessive pressure. 

In terms of analytical performances, the consequences of an insufficient vacuum are numerous and disastrous. All analyzers use a field (e.g., electromagnetic or magnetic) to separate ions according to their mass-to-charge ratios. The trajectory of the ions in the field must be as precise as possible. If the ions collide with residual molecules, they can react with them, deviate from their trajectory, and be fragmented by the collisions. These phenomena will result in resolution, sensitivity, and spectral reproducibility problems. Furthermore, residual molecules are susceptible to being ionized. The resultant ions will interfere with the characteristic ions of the analytes within the mass spectra. 

It is important to underline that a 1-1 volume under a 10 torr pressure still contains about 4.10 molecules—very far from a total vacuum. Consequently, it is impossible to avoid all collisions between ions and molecules at best, one can minimize them. 

The mass spectrometist community keeps using different international pressure units, whether they are official or not. In this book, the choice was made to systematically express pressure in torr when it directly concerns mass spectrometry and in bar in all other cases. Table 2.1 shows the conversion factors of different pressure units.  

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Other typical uses of titanium in a membrane cell process are in the pipelines for hot anolyte and in the anolyte collecting tanks as well as dechlorination systems that normally work under vacuum and sometimes limit the use of loose linings. 

Electron microscopy works under vacuum conditions because air absorbs electrons. For these reasons, wet samples cannot be analyzed by electron microscopy without previous dehydration, freezing, or freeze-drying due to the sublimation phenomena (Bache and Donald, 1998). 

As the unit will work under vacuum and a slight pressure, the sealing gland must be able to take both vacuum and pressure. As polyurethane is a very effective adhesive, the seals must be readily replaceable. If a mechanical seal is used, great care must be taken to prevent any product from coming onto a contact surface. 

The analysis in the RCM suggests that a RD process may be feasible, as the trajectories converge to the ester vertex, the highest boiler and stable node. The heteroazeotrope of water-alcohol is an unstable node, while the heteroazeotrope water-acid is a saddle. At total conversion, the temperatures at the column s ends at atmospheric pressure would be 373 K in top and about 713 K in bottom. Clearly, the last value is excessive. Here we assume a temperature below 473 K to avoid thermal decomposition, a condition that can be realized working under vacuum at 32kPa and diluting with about 12mol% alcohol. 

We have used a new cell developed by INEL FUREQUI H. This cell is attached on a standard INEL 120 diffractometer with a Cu wavelength (A = 1.54056 A). The furnace allows to heat polycrystalline samples (bulk or powder) from room temperature m to 220°C. Because of its sealed chamber, it is possible to work under vacuum (around 10" bars) or in controlled vapour flowing conditions. The inner part of the furnace is constituted by ... 

Need to work under vacuum in order to avoid the absorption of these rays by the atmosphere (the analysis of powders thus requires first pressing the powder at SO bar to form pellets). 

MALDI ionization mostly takes place in vacuum in spite of the recent development of atmospheric pressure ionization sources. Therefore, coupling a microfluidic system to MALDI-MS implies working under vacuum on the chip or performing the MS analysis off-line, i.e. introducing the microchip in the MALDI-MS once the fluidic operations are finished. Consequently, the first miniaturized developments for MALDI-MS analysis only concerned the... 

Special Chemical Methods are particularly important in cases in which impurities are difficult to remove using physical methods. In these cases, it is sometimes possible to resynthesise the substance to be purified into a material which is more readily purified. After the successful purification, the original substance must then be reconstituted. Chemical impurities can also be produced by oxygen, water, other solvents or by light, i.e. photochemically. Many organic compounds react sensitively to these influences. It is therefore often necessary to work under vacuum, in ultrahigh vacuum (UHV) or under inert gas, and to exclude light. 

In the former case the ES may have to be flashed over from time to time. This may need special equipment such as a wiped-film evaporator working under vacuum and may produce a residue that is difficult to handle. There is an alternative which may prove more economic, especially if the ES is a comparatively inexpensive hydrocarbon fraction with a high flash point. The ES containing the organic residue can be burnt as a fuel and replaced with new material. 

The process has been modified by Li et al [158] to work under vacuum, incorporating the continuous removal of AI2O3 by passing the melt through a Fiberfrax ceramic filter—less oxide will be formed under vacuum. 

For electron microscopy, it is necessary to dry the sample because the microscope works under vacuum conditions. Sample drying is usually followed by particle size reduction because of the solvent removal and particle shrinking [98]. 

Figure 5.1 Typical processes working under vacuum in chemical engineering.

A description of the application of chlorine into drinking water is given in Fig. 88. It shows a modern installation with the chlorine cylinders in a separate room, all chlorine gas pipings between cylinders and injector working under vacuum, with all measuring-, controlling- and safety devices for the dosage (System USF Wallace Tiernan). 

Using a detector that works under vacuum... 

Several of these possibilities are generally combined to achieve a spectacular decrease in analysis time. In GC-MS coupling, possibility 6 is almost never used. Possibility 7 is systematically applied insofar as the mass spectrometer works under vacuum (refer to Chapter 2). The two first options cannot be used systematically they depend on the capacity of the chromatograph used. 

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