Column

As in any chromatographic process, the column is one of the most important components of the system. It is heated to maintain the carrier gas and sample temperature constant. Small columns (up to 80 mm i.d.) are placed in an oven. Larger columns are heated by fluid circulating in a jacket. The column is made of stainless steel packed with a stationary phase. Both ends of the column are closed with metal frits.

Any type of stationary phase used in packed column analytical GC can be used for preparative pur-

Table 1 Range of temperatures and pressures used in preparative GC

Temperature (°C)

Pressure

(MPa absolute)

Column inlet

# 50 to # 300

0.1-0.5

Outlet condensers

- 20 to #100

0.02-0.15

pose. The only limitations are the cost and the availability of kilograms or tonnes of packing (e.g. a polymer of 2-6 diphenylparaphenylene oxide currently used in analytical GC is too expensive to be used on a tonne scale).

Most applications use a diatomaceous support coated with various liquid phases.

Packing the large diameter column is technologically difficult. Indeed, to be able to scale up results obtained during small scale experiments one must use 'similar' columns of any scale. 'Similar' columns means columns which have the same efficiency. This was the main difficulty encountered by the pioneers of preparative GC: their large diameter columns were inefficient compared to analytical columns and the separations obtained in the laboratory could not be reproduced for production. This problem has been solved empirically by filling the column with the stationary phase under a controlled vibration system. The packing procedure has not been published and is still the property of the column suppliers. Efficiencies of 800-1000 plates per metre are now commonly obtained. Column life times are several years longer when treated correctly - no liquid flooding and no excessive temperature.

Solar Panel Basics

Solar Panel Basics

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