Trapped materials packed

An inert gas is bubbled through the sample. The volatile hydrocarbons are transferred into the vapor phase and trapped over a sorbent bed containing 2,6-diphenylene oxide polymer (Tenax GC). A methyl silicone (3% OV-1 on Chromosorb-W, 60/80 mesh) packing protects the trapping material from contamination. Other adsorbents such as Carbopack B and Carbosieve S III may also be used. If pentane and other low boiling hydrocarbons need to be detected, the sorbent trap should be filled with activated charcoal, silica gel, and Tenax, respectively, in equal amounts. 

Figure 7.16A depicts a flexible SFE-HPLC coupled assembly developed by Ischi and Haerdi [106] that consists of three main parts [viz. the SFE system (Al), the interface (A2) and the HPLC system (A3)] each furnished with appropriate valves operating as shown in Fig. 7.16B. Thus, valve 5 in Fig. 7.16A is used to provide extraction with or without a modifier, via a tee connector on the other hand, valve 10 allows switching between static and dynamic extraction. The former is done by having the valve close the outlet of the extraction cell after the desired temperature is reached. By switching the valve back, the dynamic state is restored. Valve 13 enables trapping of the extracted analytes, either on a C, silica column placed in an oven for on-line preconcentration and insertion of non-polar or low-polar analytes into the chromatograph after elution or into a liquid phase to implement an off-line operation. When polar ionic analytes are to be preconcentrated, the eluent from the extractor is diverted to valve 18 and retained on the ion-exchange material packed in the column. Preconcentration of both non-polar, low-polar and polar ionic analytes can be accomplished by using both valves (13 and 18) [106],...

Realisation of the first approach - trapping and offline analysis - employs a miniature gas-sampling tube packed with a mixture of Tenax (molecular sieve) and Carbopak (activated charcoal) absorbent material. Such tubes are routinely used for environmental monitoring of hazardous industrial atmospheres whereby operators during the normal course of their duties carry a small tube (about the size of a pen) clipped to their clothes. A pump may be used to draw gas through the tube at a controlled rate and, at the end of the work period, the tube is sealed and sent for analysis. Heating the sorbent tube drives off the trapped material into a gas chromatograph for separation and quantification. 

Dicblorodifluoromethane (Freon 12) 175-71-8] M 120.9, m -158", b -29.8"/atm, 42.5"/10atm. Passage through saturated aqueous KOH then cone H2SO4, and a tower packed with activated copper on Kielselguhr at 200° removed CO2 and O2. A trap cooled to -29° removed a trace of high boiling material. It is a non-flammable propellant. 

The particle size of the packing material is smaller than 80 mesh and larger than 100 mesh. In other words, it is the material that passed through the 80-mesh screen and was trapped on the 100-mesh screen. 

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