Adsorption capillary columns

The determination of traces of polar compounds is a very important application of adsorption capillary columns. For example, gas chromatographic analysis of hydrogen sulfide is often performed on polymer adsorbents (for example, Porapak Q, N or QS [39-44]). However, other adsorbents and stationary phases have been also used (Carbopack [45, 46], Triron X-305 [47- 8], Tenax GC [49], polyphenyl ether [48, 50] and various methyl silicone phases [51, 52]). Determination of hydrogen sulfide on WCOT columns has been performed with non-polar or medium polar silicone phases at sub-ambient temperatures [53-55]. 

On our opinion, equation (3-8) can be used for adsorption capillary columns, if F is the ratio of the solid phase volume to the surtoce of the... 

Fig. 3-3 Efficiency characteristic VH vs. sample size for adsorption capillary column with aluminum oxide layer on the inner walls [26], splitless (a) and split-type (b) sample injection technique.

Fig. 3-3 shows the H-W dependence according to equation (3-21) for the same adsorption capillary column but with the use of different sample injection techniques, viz., split-type (b) and splitless (a). It is evident that the dependence of the HETP value on sample size in these coordinates is linear, which is corroborated by equation (3-21). When a splitter is used, the efficiency shows a market increase (the H value decreases). 

An example of the separation of a methane-iso-butane-n-butane mixture with splitless injection of 0.5 ml of the sample into a glass capillary column with a silica layer is given in paper [26]. The analysis time is less than 1 min. Incidentally, splitless injection of a sample was already used in an earlier period of adsorption capillary column development (see, for example, Fig. 3-4 [70]). 

In our opinion, it is possible to use adsorption capillary columns without a splitter to solve many practical problems. 

Active solid adsorbents are utilized not only in pure form but also after modificatton, usually carried out with low volatility organic compounds (see, e.g. [4, 9, 10]). This section contains some examples of the use of adsorption capillary columns with modified adsorbents. 

Rg. 5-34 Chromatogram of C1-C4 hydrocarbon gases on an adsorption capillary column with alkaline treated walls [124],... 

A classification of the available methods for adsorption capillary column preparation is presented in Fig. 6-1 [1]. 

Apparatus for preparation of adsorption capillary columns by the high-pressure static method... 

Starting with the early attempts at adsorption capillary column production, adsorbents were obtain directly in the column by chemical reaction. The potential advantages of such a method are as ifollows the adsorption layer can be prepared without using suspensions and with homogeneous reagents readily filling the entire column and being removable from it. Moreover, chemical reactions can be repeated in order to increase layer thickness. 

The method of adsorption capillary column preparation by means of in situ synthesis of sorbents is only applicable to a limited number of adsorbents, but it does allow two problems to be solved simultaneously 1) sorbent formation 2) binding of a sorbent to the inside surface of capillary. 

In our opinion, the suspension method is the most universal for gas adsorption capillary column production. The main unsolved problem is the binding of adsorbent to the capillary inside walls methods of binding and binding agents must be selected individually. 

The field of practical application of adsorption capillary columns is in a state of continuous dev -opment. These columns are utilized to great advantage in the gets, chemical and petrochemicetl industries, environmental analysis, etc. 

The theories of retention and efficiency (HETP) reflect the main features of adsorption capillary columns. 

In the future it should prove worthwhile to pay more attention to the development of fields of gas adsorption capillary chromatography such as adsorption capillary columns in multidimensional gas chromatography, adsorption capilleuy columns with nonporous (or slightly porous) inner surfaces, theory of separation, optimization, application of modified... 

Several gas-solid adsorption capillary columns are available. They are commonly called porous-layer open tubular or PLOT columns. These columns contain a layer of adsorbent particles coated on the irmer wall of the fused silica tubing. Phases of aluminum oxide (alumina), molecular sieves, and porous polymers (Poraplot-like) are commercially available. Gas-solid adsorption rather than a gas-liquid partition is the separation mechanism involved. PLOT columns are well suited for the analysis of light hydrocarbons, sulfur gases, permanent gases, or other very volatile solutes at or... 

Gas-Solid Adsorption Capillary Columns (PLOT Colnmns)... 

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