Cryogenic oven trapping

A. Ishii, H. Seno, K. Watanabe-Suzuki, O. Suzuki and T. Kumazawa, Determination of cyanide in whole blood by capillary gas chromatography with cryogenic oven trapping, Anal. Chem., 70, 4873-4876 (1998). 

Another way to increase sensitivity is to increase the volume injected into the column. Lowering the temperature of the entire column in cryogenic oven trapping (COT) methods or for the injection port at the inlet of the column in cryogenic focusing (CF) methods allows the injection of as much as 10 times the typical sample volume. Liquid nitrogen or liquid carbon dioxide is used to lower the temperatures to well below 0 °C (—180 °C for nitrogen and 90 °C for carbon dioxide). These techniques result in better peak shapes in addition to increased sensitivity. 

Watanabe-Suzuki, K Seno, H. Ishii, A Kumazawa, T. Suzuki, O. (1999). Ultrasensitive method for the determination of ethanol in whole blood by headspace capillary gas chromatography with cryogenic oven trapping. Journal of chromatography B. 727,89-94... 

Watanabe-Suzuki K, Nozawa H, Suzuki O, and Ishii A (2003) Sensitive analysis of alkyl alcohols as decomposition products of alkyl nitrites in human whole blood and urine by headspace capillary GC with cryogenic oven trapping. Journal of Chromatographic Science 41 63-66. 

A capillary column, 30 m or longer, with a thick film of stationary phase, offers an alternative to cryogenic oven temperature control for solute-focusing purposes, which is especially attractive with auxiliary sample introduction techniques of purge and trap and thermal desorption. 

If the sample is small enough or the sorbent on which it is trapped is of sufficiently low thermal mass, the sample can be heated rapidly. Commonly, however, sample heating is slow enough that the desorbed material must be cold-trapped at the head of the column by the use of either a cold trap or a cryogenic oven. This is essentially a two-step desorption (1) the sample is desorbed from the sorbent trap and (2) it is recondensed on the column and is desorbed as the temperature program proceeds. There are numerous configurations and types of equipment available for thermal desorption. These have been recently reviewed by Hinshaw (129) and Wampler (130). 

Fig. 7.2. Schematic diagram of a straightforward supercritical fluid extractor. 1 extracting fluid source, 2 extractant propulsion unit, 3 modifier reservoir, 4 modifier propulsion unit, 5 oven, 6 equilibration coil, 7 chamber containing the thimble or sample cell, 8 back-pressure regulator, 9 collection system (A bubbling, B sorption, C cryogenic trapping).

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