Topics in..
. Chemical Instrumentation
Edited by 5. Z . LEWIN. N e w York Universitv, N e w York 3, N . Y .
These articles, most of whieh are to be cont~butedk azlest authors, ore inlended lo serue ihe read& of this JOURNALb y calling a&&on lo new daelooments in the theow, desian, or availabililv of chemical loboralow instrumenlat~on,05 by present& useM insighla a& eiplanations of top& that are of p~aclicalimportance to those who use, or teach the use of, m o b instrumentation and instncmalal techniques.
XVII. Apparatus for Large Scale Gas Chromatography Ernrt Bayer, Chemisches lnsfifut der UniverrifGt, Tiibingen, Germany. Translofed from the German by S. Z. Lewin
Gas chromatography was originally developed and applied aa a purely analytical methad. I n the intervening years, however, i t has been shown that this method can also be applied to the preparativescale production of substances. I n fact, the techniques of preparative-scale gaa chromatography have even adwnced already to the orders of magnitudes of samples that are characteristic of certain industrial-scde sepmtrtltions. Further development of continuous processes baaed upon gas chromatography will lead to even greater utilization of these techniques on an industrial scale. The present discussion will, however, be limited to those types of preparative gas chromatography that me of direct relevance to laboratory work. I n this regard, one may distinguish t a o characteristic classes of application: 1. The preparative separation of substances for subsequent additional identification and investigation, e.g., by elementary analysis, spectra, or nuclear resonance studies. For this purpose, samples of the order of from 1 to 1000 mg are needed. 2. The preparative separation of substances for purification from intermediate or end products. In this case, the requirement is for the separation of quantities of from 1to 200 g. Although the first class may he considered to be equivalent to the analytical field with respect to the final objective m d sample size, the second category is in every respect a unique technique. These different requirements have been reflected in the development of different forms of instrumentation, Hence, there are, s t the present time, essentially two established techniques of preparative gas chromatography. In the first, the apparatus retains essentially the dimensions
of normal, analytical gas cbmmatography with columns of 1-1.5 em diameter. In order to obtain larger quantities, one carries out remated se~arationsof small quantities. As instrumental sccessories, a special injection device, and a. repet,itive collection arrangement are necessary, so that the repeated measurement out and introduction of samples and the collection and collation of the separated fractions can be controlled in a completely automatic fashion. (Instrumentation for this class uf techniques are produced, ~~~
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However, aa a consequence of the limitation of the column diameter, an arbitrary limit is placed on the amount of specimen that can heseparrsted. This is not the ease with the more universal second approach. This technique is based upon the experimentally established fact that upon increasing the column diameter, the resolving power does not decrease significantly (1-3). Thus, the plate heights (height equivalent to a theoretical plate, HETP) of columns with 1&25 cm diameters still lie in the vicinity of 0.3 cm (1-4). The capacity of a, column of 10 em diameter is, however, 100 times greater t'r2.n that
