Degassing Methods

Degassing of the eluent is important for trouble-free operation and highly sensitive detection,2 otherwise the eluent may become supersaturated with air that is released as bubbles in the pump check valves or the detector flow 

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For oxidative detection removal of dissolved air from the mobile phase is necessary to prevent air bubble formation at the column outlet, which disturbs the electrolysis process. Vacuum filtration usually is sufficient to remove enough air for bubble-free operation. However, air readily redissolves in the mobile phase. Continuous helium sparging is therefore the only effective degassing method for longer periods. 

The suitability of the media degassing method. The formation of bubbles during the dissolution process can affect the rate of release of the active ingredient. 

Fluxing and degassing methods, combined with filtration, to give highest quality aircraft and other critical alloys. 

Nonlinear and dynamic models of desorption are used in the sequel. Mathematical justification of the boundary-value problems for the TDS-degassing method of metal saturated with hydrogen is given in [6,7]. The work [4] was a starting point of the results presented here. Algorithm of parameter identification for the model of hydrogen permeability of metals for the concentration pulses method [5] is presented in [8],... 

Degassing method (Waters Eluent Stabilization System, MiUipore Corp., Milford, MA, USA)... 

Input information such as files or documents is essential for the execution of an activity. Depending on the quality or type of the information, an activity cannot start or it must be executed differently if information is missing. For example, Activity 14 in Fig. 5.12 requires some information about degassing methods as well as information about the chemical components involved and their thermodynamic properties. Based on this information, an expert generates alternatives for the separation such as a wiped-film evaporator or a leacher. Both methods are analyzed in more detail (Activities 18 and 22). 

In the following two figures, you can see the efficacy of the four most important degassing methods for a polar (methanol. Figure 5-1 left) and a non-polar (hexane, Figure 5-1 right) mobile phase system. 

Figure 5-1. Efficacy of degassing methods for a polar (MeOH) and a non-polar (hexane) solvent. (Source J W Dolan, L R Snyder, Troubleshooting LC Systems, Human Press, 1989)...

Figure 10.17a shows the impact of the degassing conditions on the SSA of anhydrous portland cement. When the degassing is conducted under vacuum and/or at temperatures higher than 40°C, a partial or total dehydration of gypsum occurs involving an increase in the SSA (see Figure 10.17b). Mantellato et al. (2015b) proposed degassing anhydrous cement samples at 40°C under N2 flow for 16 hours as an optimum degassing method, since cement composition is preserved. When using this protocol, reproducible results with a scatter of less than 5% can be obtained.

The above batch process has undergone numerous refinements to improve yields, processing characteristics, purity, and storage stabiUty, but it remains the standard method of manufacture for these products. Recentiy a continuous process has been reported by Bayer AG (6) wherein the condensation is carried out in an extmder. The by-products are removed in a degassing zone, and the molten polymer, mixed with stabilizers, is subsequendy cracked to yield raw monomer. 

Ladle metallurgy, the treatment of Hquid steel in the ladle, is a field in which several new processes, or new combinations of old processes, continue to be developed (19,20). The objectives often include one or more of the following on a given heat more efficient methods for alloy additions and control of final chemistry improved temperature and composition homogenisation inclusion flotation desulfurization and dephosphorization sulfide and oxide shape control and vacuum degassing, especially for hydrogen and carbon monoxide to make interstitial-free (IF) steels. Electric arcs are normally used to raise the temperature of the Hquid metal (ladle arc furnace). 

In the dynamic method the powder is flushed with an inert gas during degassing, nitrogen is then adsorbed on the powder in a carrier of helium gas at known relative pressure while the powder is in a container surrounded by hquid nitrogen. The changing concentration of nitrogen is measured by a cahbrated conductivity cell so that the amount adsorbed can be determined. 

Sufficient data are not yet available to allow evaluation of the relative merits of palladium-on-carbon and degassed Raney nickel catalysts. Comparable yields of 2,2 -biquinolines have been obtained by both methods under suitable conditions but the percentage conversions with degassed Raney nickel have been found to be much lower, reflecting the extent of side reactions with this catalyst. However, work in this laboratory has shown that the reaction of quinoline with palladium-on-carbon is not free from complications for example, at least three products in addition to 2,2 -biquinoline have been detected by paper chromatography. 

Assay of pholasin. Two different methods have been used. In the first method, light intensity or total light emission is measured when a standard solution of luciferase is added to a pholasin sample (Henry et al., 1970). In the second method, total light emission is measured when 1 ml of a degassed solution of 0.3 mM FeSC>4 is injected into 2 ml of 0.15 M phosphate buffer, pH 7.0, containing a pholasin sample and 0.75 M NaCl (Michelson, 1978). The luminescence reaction is complete within 2 or 3 min. 

The method uses the adsorption isotherm and the expt details of determining this may be summarized as follows (1) the powder under investigation is thoroughly degassed in a vacuum ... 

Although the method is simple and straightforward, there are a few important points to consider. First, since 200 pL are being injected on to a 2-mm diameter HPLC column, compatible solvents must be injected on to the column and the amount of acetonitrile used in the prepared samples should be exactly as directed. Second, the temperature of the column and the use of a degassing system for the mobile phase are critical components required to guarantee reproducible chromatography. In addition, the standards should be stored in a refrigerator when not in use. 

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