Sample inlets open tubular columns

The gas chromatograph was equipped with a flame ionization detector. A 50-foot length of 0.020 inch i.d. stainless steel open tubular capillary column coated with Carbowax 1540 served as the main column. A freeze out trapping technique was used to concentrate the a-pinene before entering the main column. The pre-column trap consisted of an in-line capillary column, identical to the main one, inserted between the injector and inlet of the main column. The trap was located outside the oven and cooled with a dry ice-ethanol bath before injection of a 5 cc sample. A 80°C hot water bath was used to release the a-pinene. The operating conditions of the gas chromatograph were as follows ... 

The first of the separation techniques to be used in process measurement was gas chromatography (GC) in 1954. The GC has always been a robust instrument and this aided its transfer to the process environment. The differences between laboratory GC and process GC instruments are important. With process GC, the sample is transferred directly from the process stream to the instrument. Instead of an inlet septum, process GC has a valve, which is critical for repetitively and reproducibly transferring a precise volume of sample into the volatiliser and thence into the carrier gas. This valve is also used to intermittently introduce a reference sample for calibration purposes. Instead of one column and a temperature ramp, the set up involves many columns under isothermal conditions. The more usual column types are open tubular, as these are efficient and analysis is more rapid than with packed columns. A pre-column is often used to trap unwanted contaminants, e.g. water, and it is backflushed while the rest of the sample is sent on to the analysis column. The universal detector - thermal conductivity detector (TCD)-is most often used in process GC but also popular are the FID, PID, ECD, FPD and of course MS. Process GC is used extensively in the petroleum industry, in environmental analysis of air and water samples" and in the chemical industry with the incorporation of sample extraction or preparation on-line. It is also applied for on-line monitoring of volatile products during fermentation processes" ... 

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