Reaction Gas Chromatography Techniques

Polymers being solid substances, with a few exceptions, cannot be directly analysed using gas chromatography (GC). However, it is possible by the application of well-controlled chemical reactions to decompose polymers to simpler volatile snbstances that are amenable GC and thereby one can obtain information concerning the original polymer. 

A further special case of reaction gas chromatography (RGC) involves pyrolysis (or photolysis) of the polymer in the absence of oxygen and examination of the volatiles produced by gas chromatography to provide information on the structure of the original polymer. 

Further complementary techniques can be applied to obtain even more information. Thus RGC can be coupled with mass spectrometry (MS) or nuclear magnetic 

There are three broad catagories of reaction gas chromatography  

Reaction of the polymer with a suitable reagent followed by analysis of the reaction products by, for example, GC, MS or another relevant technique (see Section 5.1.1). 

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A suitable technique for this purpose (concentration of trace components and their isolation in a new reaction) involves the use of a liquid bubbler. The applicability of this technique in analytical reaction gas chromatography was shown earlier [15] using as an example the preliminary concentration of hydrogen sulphide and carbon dioxide by means of an alkaline solution of sodium hydroxide through which a flow of the sample gas was passed. When the solution was acidified, the acidic traces formed a concentrated zone, and were separated on a chromatographic column. A liquid bubbler as illustrated in Fig. 8.3 was used to concentrate the trace components. 

The hydrolysis-gas chromatography technique applied to copolymer analysis has already been described in the literature and is accurate to within about 2%. However, it contains a systematic error in that it is difficult to ensure complete conversion of the monomer units to their respective methyl esters and some dehydration to the corresponding or,)3-unsaturated ester (e.g. hydroxybutyrate to crotonate) usually occurs. The liquid chromatography technique suffers from similar problems but the hydrolysis to free acid using perchloric acid tends to be a cleaner reaction than methanolysis and it is our experience that comonomer ratios can be determined with an accuracy better than 1%. 

The technique of potassium hydroxide fusion-reaction gas chromatography has been applied to the determination of alkyl and aryl groups in polysiloxanes. The method involves the quantitative cleavage of all organic substituents bonded to silicon, producing the corresponding hydrocarbons ... 

Schleuter and Siggia [69-71] and Frankoski and Siggia [72] used the technique of alkali fusion reaction gas chromatography for the analysis of imide monomers and aromatic poiyimides, polyamides, and poly(amide-imides). Samples are hydrolysed with a molten potassium hydroxide reagent at elevated temperatures in a flowing inert atmosphere ... 

This modified catalyst capillary was applied in on-column reaction gas chromatography. As this efficient technique combines catalysis and analysis in one single step, in situ reaction monitoring is possible. 

Various workers have appied the technique of reaction-gas chromatography to the determination of organic substituents bonded to silicon. These are summarized in Table 90. 

Reaction gas chromatography 58—61) has become one of the most convenient methods for performing chemical reactions at the microgram level. In this technique, the unknown compound is injected into the GC system and is retained or transformed, frequently at the injection port on a precolumn. The products that elute can be collected and analyzed. 

A derivatization technique is commonly applied to an agrochemical with certain reactive functional groups (e.g., carboxylic acid, amine, phenol) to make the compound amenable to either gas chromatography (GC) or LC analysis. An in-depth discussion of derivatization reactions used in the analysis of agrochemicals is beyond the scope of this article. For more information on this topic, the reader is referred to Knapp. °... 

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