Gas Chromatography - The Column Oven and Temperature Programmer > Page 36

Figure 21. The Separation of Some Chiral Amines

An example of the use of a proprietary modified cyclodextrin in the separation of some chiral amines is shown in figure 21. It is seen that excellent separations were obtained. A G-PN column was used which was 30 m long and 0.25 mm I.D. and operated at 130˚C employing helium as the carrier gas. The basic materials are patented and the technique of bonding and coating the material onto the column is extremely difficult and involves much proprietary art.

The Column Oven and Temperature Programmer

The column oven should operate over a fairly wide temperature range (e.g. from 5˚C to 400˚C). In practice, however, the maximum oven temperature needed is usually less than 250˚C, particularly when synthetic stationary phases are being used, as many of them tend to be unstable and either decompose or volatilize at higher temperatures. Similarly, initial temperatures below 50˚C are also rarely needed. The oven usually has air circulation driven by a powerful fan to ensure an even temperature throughout the oven. The temperature in any part of the oven should be stable to 0.5 ˚C and when operating isothermally the column temperature should be constant to 0.2 ˚C. The oven should have a capacity of 1-2 cu. ft. and is supplied with fittings to accept more than one column and some switching valves if so desired. Such equipment is needed for multidimensional chromatography.

The temperature programmer (hardware and software) usually has a range of linear gradients from 0.5˚C/min. to about 20˚C/min. Some programmers include nonlinear programs such as logarithmic and exponential, but most GC analyses can be effectively accomplished using linear programs only. The program rate can be changed at any time in the chromatographic development or intermittent isothermal periods can be inserted where necessary in the program. The temperature programming limits are usually the same as those of the oven (viz. 5˚C to 400˚C). All connections between the column and the detector, that pass though the column oven wall to the detector oven, are supplied with their own heaters so that no part of the conduit can fall below the column oven temperature. A cool spot in the conduit will cause condensation which can result in broad and distorted peaks.