Low-Pressure Gas Chromatography with Split Injection and Photoionization Detection

The advantages of low-pressure gas chromatography (GC) are discussed. The performance of a commercial photoionization detector (PID) operated at subambient pressure is evaluated using a GC system designed for high speed, vacuum outlet operation. At atmospheric pressure, use of the PID results in significant band broadening relative to a flame ionization detector (FID) for elution times of a few seconds. Even with the use of 50 mL/min makeup gas, excessive band broadening occurs with the PID. At a pressure of 10 Torr, use of the PID results in no significant band broadening, and greater resolution is achieved than with the FID operated at atmospheric pressure for similar retention times. Chromatograms are presented showing the effects of outlet pressure and makeup gas flow rate on PID performance.