Solvent vapor removal

Activated carbon columns are frequently used to remove trace or dilute organic impurities from an inert nonadsorbing gas. These impurities may consist of toxic compounds, odor-forming compounds, solvent vapors, volatile organic compounds, etc. A TSA process is generally used for these applications. However, both TSA and PSA processes are used for the particular application of solvent vapor removal and recovery which are described in Section 22.4.1.1... 

An intermediate calculated result is the ratio of the volume of solvent vapor (removed from the vapor degreaser with the parts basket) divided by the volume of the room. This is the vapor phase concentration of solvent. For simplicity, it is also assumed that the room ventilation rate maintains this concentration. 

Solvent vapor removal from exhaust gases... 

In many applications in mass spectrometry (MS), the sample to be analyzed is present as a solution in a solvent, such as methanol or acetonitrile, or an aqueous one, as with body fluids. The solution may be an effluent from a liquid chromatography (LC) column. In any case, a solution flows into the front end of a mass spectrometer, but before it can provide a mass spectrum, the bulk of the solvent must be removed without losing the sample (solute). If the solvent is not removed, then its vaporization as it enters the ion source would produce a large increase in pressure and stop the spectrometer from working. At the same time that the solvent is removed, the dissolved sample must be retained so that its mass spectrum can be measured. There are several means of effecting this differentiation between carrier solvent and the solute of interest, and thermospray is just one of them. Plasmaspray is a variant of thermospray in which the basic method of solvent removal is the same, but the number of ions obtained is enhanced (see below). 

Solutions can be examined by ICP/MS by (a) removing the solvent (direct and electrothermal methods) and then vaporizing residual sample solute or (b) nebulizing the sample solution into a spray of droplets that is swept into the plasma flame after passing through a desolvation chamber, where excess solvent is removed. The direct and electrothermal methods are not as convenient as the nebulization inlets for multiple samples, but the former are generally much more efficient in transferring samples into the flame for analysis. 

The large quantities of solvent vapor produced from the evaporating droplets must be removed before reaching the plasma flame, which is done by having cooling tubes sited after the heated desolvation chamber to condense the vapor into liquid. This condensed liquid is run to waste. 

Evaporation and Distillation. Steam is used to supply heat to most evaporation (qv) and distillation (qv) processes, such as ia sugar-juice processiag and alcohol distillation. In evaporation, pure solvent is removed and a low volatiUty solute is concentrated. Distillation transfers lower boiling components from the Hquid to the vapor phase. The vapors are then condensed to recover the desired components. In steam distillation, the steam is admitted iato direct coatact with the solutioa to be evaporated and the flow of steam to the condenser is used to transport distillates of low volatiHty. In evaporation of concentrated solutions, there may be substantial boiling poiat elevation. For example, the boiling poiat of an 80% NaOH solution at atmospheric pressure is 226°C. 

Charcoal Tubes Reference has been made earlier to adsorption, which is the property of some solid materials, such as activated charcoal, to physically retain solvent vapors on their surfaces. In environmental health testing, the adsorbed vapors are removed, generally with a solvent, in a laboratory. The solvent is then analyzed by physical methods (gas chromatography, etc.) to determine the individual compounds whose vapors, such as benzene, were present in the sampled air. Industrial atmospheric samples can be collected in small glass tubes (4 mm ID) packed with two sections of activated charcoal, separated and retained with fiberglass plugs. To obtain an air sample, the sealed ends of the tube are broken off, and air is drawn through the charcoal at the rate of 1 liter per minute by means... 

An excellent example of PLC applications in the indirect coupling version is provided by the works of Miwa et al. [12]. These researchers separated eight phospholipid standards and platelet phospholipids from the other lipids on a silica gel plate. The mobile phase was composed of methylacetate-propanol-chloro-form-methanol-0.2% (w/v) potassium chloride (25 30 20 10 10, v/v). After detection with iodine vapor (Figure 9.2), each phospholipid class was scraped off and extracted with 5 ml of methanol. The solvent was removed under a stream of nitrogen, and the fatty acids of each phospholipid class were analyzed (as their hydrazides) by HPLC. The aim of this study was to establish a standardized... 

In addition to tobacco smokers, individuals who have had previous exposure to materials containing methylene chloride, such as degreasers, solvents, paint removers, and furniture strippers, are at greater risk because of an existing body burden of carbon monoxide. Approximately one-fourth to one-third of inhaled methylene chloride vapor is metabolized in the liver to carbon monoxide. In addition, methylene chloride is readily stored in body tissue. This stored material is released over time and results in elevated levels of carbon monoxide for extended periods, in some cases more than twice as long as compared with direct carbon monoxide inhalation. 

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