Gas flow-cold trap method

Fig. 9.4.2 Size histogram of In small particles produced by a gas flow-cold trap method in acetone. The pressure of He and Ar mixed gas was 1.3 kPa. The ordinate represents the number of samples at a given size interval. Tolal number of samples, 250. Broken line, calculated curve from the lognormal distribution with a = 2.13 and d = 20 nm. (From Ref. 4.)...

Fig. 9.4.8 Apparatus for the gas flow-cold trap method. One of the gas inlets is abbreviated in the figure. A cover in the figure is used to improve a collection yield. Without this, the particles produced just above a crucible are drifting in the chamber to deposit on the chamber wall. The end of the gas line is evacuated by a rotary pump so as to constantly flow the carrier gas. A solvent feeder is inserted on the gas line for the sublimation of organic liquid to deposit at the trapping apparatus cooled with liquid nitrogen. (From Ref. 10.)...

In the preceding section, we emphasized that the surface interaction of metallic particles with liquid molecules is a very important parameter in the dispersion behavior of the sol. Since the surface nature is very sensitive to the surface modification, we can easily regulate it with the use of surfactant. As seen in Figure 9.4.23, almost all metallic particles cannot be dispersed in hexane as a suspension liquid. In this section, we show what kind of surfactant is effective in dispersion. The sample was prepared by the gas flow-cold trap method. We tested three surfactants, dimethyldi-... 

Thermal Desorption Thermal desorption is an alternative GC inlet system particularly used for VOC analysis. However, the analytes subjected to thermal desorption must be thermally stable to achieve successful analysis. Otherwise, decomposition occurs. This technique is mainly used for determination of volatiles in the air. Such a methodology requires sample collection onto sohd sorbents, then desorption of analytes and GC analysis. Traditionally, activated charcoal was used as a sorbent followed by extraction with carbon disulfide. However, solvent desorption involves re-dilution of the VOCs, thus partially negating the enrichment effect. Therefore, the sampling method is to pump a sample of gas (air) through the sorbent tube containing certain sorbents in order to concentrate the VOC. Afterwards, the sample tube is placed in thermal desorber oven and the analytes are released from the sorbent by application of high temperature and a flow of carrier gas. Additionally, desorbed compounds are refocused in a cold trap and then released into the GC column. Such a two-step thermal desorption process provides a narrow chromatographic band at the head of the column. 

This Section Ls restricted to a description of some of the work of Ander-gon, 8-a> who has ably applied the quantitative analysis of vapors by infrared spectroscopy to analytical problems in carbohydrate chemistry, principally to the Zeisel alkoxyl determination. In this particular application, the usual Zeisel apparatus was used, and the volatile iodide liberated was carried by a flow of nitrogen into a cold trap where it was collected quantitatively Anhydrone (magnesium perchlorate) was used for removing water vapor which would otherwise interfere in the spectrum. The contents of the trap were allowed to vaporize into an evacuated gas-cell, and air was then admitted through the trap to sweep all the vapor into the gas-cell. Double-beam compensation of atmospheric water vapor and carbon dioxide was not upset by this procedure, which also served the purpose of increasing the sensitivity of the infrared method by the well known pressure-broadening effect. The complete spectrum of the vapor... 

A third sample preparation method is purge and trap, which aims to extract as close to all of the analyte as possible from the solid or liquid sample and is a deviation from headspace sampling. It works by bubbling a purge gas such as helium through the heated sample vial. The gas carries analyte up into an adsorption tube packed with selective stationary phase. After all the analyte has been trapped in the tube, the gas flow is reversed through the tube to remove any residual solvents. The tube is then directed to the injector port and, heated to desorb the analytes, which are then cold-trapped onto the head of the GC column. From there, the concentrated sample is heated for GC separation. 

D. (3-5) Rely on cold-trapping and then rapid healing of the column segment for the collect/expel process. The heating may be provided by a secondary heated gas flow, or just the stirred oven. (6 and 7) Are valve-based sampling methods which subsample the peak from D into D. 

Samples are hydrolyzed with a molten potassium hydroxide reagent at elevated temperatures in a flowing inert atmosphere. Volatile reaction products are concentrated in a cold trap before separation by gas chromatography. The identity of amine and/or diamine products aids in the characterization of the monomer or polymer the amount of each compound generated is used as the basis for quantitative andysis. The average per cent relative standard deviation of the method is + 1.0%. 

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