Subambient Oven Temperature Control

Many HPLC instruments are already furnished with temperature controls for the column. Unified chromatography requires a much wider temperature range than is currently practiced in HPLC. Until better defined by experience, a temperature range from about —60 to about 350°C seems reasonable as a specification. Since this is well in the range of a GC oven with subambient temperature capability, no new technology is required. 

Separations in gas chromatography are carried out within the temperature limits from about — 100°C to 450°C. Purpose-built instruments are usually required for high-temperature operation between 375°C and 450°C. Subambient temperature operation using the boil over vapors from Hquid nitrogen or carbon dioxide for cooHng is available as an option for standard instruments. The oven temperature is adjusted using an electrically controlled solenoid valve to pass coolant into the oven where it is mixed with air and then circulated at high velocity. 

Most gas ehromatographs have the capability to operate the column oven at subambient temperatures. An accessory kit is available for either liquid nitrogen (—99°C) or carbon dioxide (—40°C) as a coolant and includes a cryogenic valve that is mieroprocessor controlled. The valve opens and closes, depending on the demand for coolant. In the open position, coolant is sprayed into the oven, where it chills the oven down with assistance from forced-air convection. 

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