Carrier Gas Method

Various methods using a gas chromatograph allow measurement of the flux of gas diffusing through the membrane [I]. 

The dish method [1] is used for measuring the permeability of vjpjrs, by detecting the quantity transmitted by change in weight. Such a method is detailed in ISO 2528 [26] for sheet materials in general and also in ISO RII95 [27] for plastics film and thin sheets. 

---

Many carrier gas methods were reviewed in detail by Lomax2, 3. Apparatus using the measurement of thermal conductivity to estimate permeability has been described, for example, by Yasuda and Rosengren10... 

The protonated cluster ions were observed to be the major product ions in the CMS of ammopia, water, etc., although unprotonated cluster ions have also been observed in these cases, depending on the choice of carrier gas, method of ionization, and electron energy utilized in the investigation (Shinohara et al. 1985, 1986). The inability to observe unprotonated cluster ions is usually attributed to poor Franck-Condon factors for the vertical ionization transitions. These poor Franck-Condon factors arise from the large differences in the configuration of the neutral and ionic clusters (Stace 1987a). 

If a volatile monomer is used in an ADMET polymerization, a condenser should be used to return monomer vapor to the reaction mixture. The kinetics of step-growth polymerization dictate that the concentration of monomer falls very quickly to produce dimer, trimer, and so forth. Nevertheless, monomer will be present for some time after the start of the polymerization. If the monomer is particularly volatile, a dry ice-isopropanol condenser is useful. This can be constructed in any glass shop by attaching a cup-shaped cooling reservoir to a vacuum valve or other cylindrical glass tube with the required joints and valve. If the monomer is only slightly volatile, or the carrier gas method is used, a water-cooled condenser is sufficient to retain monomer in the flask, while allowing ethylene to escape. 

It has recently been demonstrated that ADMET occurs in the solid state. If the ADMET of 1,9-decadiene is carried out at temperatures below 60°C, the polyoctenamer will solidify after an average DP of about 5 is reached. Using the carrier gas method, ADMET continues in this solid for days as proven by GPC analysis. In some cases molecular weights of greater than 70 kDa with complex 10 have been observed by this method. It is not a general method, however, and the scope and limitations are still being explored [106]. 

The so-called carrier-gas method is the most complicated approach to gas permeation monitoring.19 Either pure-component or multicomponent permeation rates through Alms can be monitored using this device, shown in Fig. 20.3-8. A carrier gas such as helium, containing a desired partial pressure of the desired component or components. Hows past the upstressu face of the membrane. A downsttesm sweep gas picks up the permeated components and routes them to a gas chromatograph for analysis of the fluxes of each penetrant. An excellent discussion of such a system has been offered by Pye el al.and comparisons were made with manomeiric cells for pure gas permeation to prove that the results for both celts are essentially identical if care is taken in operation. 

This report describes a carrier-gas method for measuring vapom pressure of liquid metals. Vapour pressiues of nickel were determined at temperatures 1813 to 1893 K. The results can be represented by the following equation logioPmm = -21030/r + 9.689, where is vapour pressure (in mm of Hg). The heat of vaporisation of nickel at 0 K was determined to be 427.898 kJ mol . ... 

Carrier gas techniques are commonly referred to as dynamic because gas is permitted to flow across each side of the test specimen, at equal pressure. The gas transmission cell is similar to those of the previous methods, in that the test piece forms a barrier between two chambers. In the most basic of carrier gas methods the test gas flows at a constant rate through one chamber and a second gas, the carrier, flows through the other chamber at a constant rate. Test gas permeates through the sample and is swept away to a detector by the carrier gas. The detector may be of the absorptiometric [33] or of the thermal conductivity type [34,35], although other detectors have also been used. 

For gas permeation measurement, there are three concepts of conditions test methods. First is a constant volume, second is a constant pressure and third is a carrier gas method. 

The carrier gas method such as ASTM D 3985 is the commonly used for film oxygen permeability test. The test gas, oxygen flows on one side of the test piece and a second gas, nitrogen as carrier gas, flows on the other side and is quantitatively analysed to determine the quantity of test gas which has passed... 

Methodology. In the case of gas adsorption isotherms, the equilibrium concentration is given by the relative pressure plpo), which is the equilibrium pressure p divided by the saturation pressure po of the adsorbate at the temperature of the measurement. S/G adsorption isotherms are determined typically by step-by-step volumetric and gravimetric or by continuous dynamic (carrier gas) methods (1,2). The conditions of sample preparation (outgassing temperature, duration) should be chosen carefully to remove all the contaminants but nevertheless preserve the identity of the adsorbent. 

The first comprehensive investigations using reducing fusion were published by Kraft and Kahles (88), employing the argon carrier gas method. 

---