Effect of vacuum on the performance of the flame ionization detector used for vacuum‐outlet gas chromatography

Vacuum-outlet operation of short fused-silica open tubular columns for gas chromatography provides benefits to analysis speed by increasing the optimum velocity while minimizing the loss in resolution. Vacuum-outlet operation of a column with a gas chromatographic detector necessitates that the detector also be under vacuum. Simple modifications were made to a gas chromatograph–flame ionization detector (GC–FID) for vacuum-inlet and vacuum-outlet operation. The vacuum-inlet system was operated in the splitless mode to allow for efficient sample loading prior to operation at reduced pressures. The goal of FID operation at 100 torr or less was achieved by using oxygen in place of air and optimizing the gas flows under vacuum to maintain a stable flame at pressures as low as 46 torr. An outlet pressure of 85 torr with optimized gas flows allowed for routine operation of the FID without solvent flame-out. It was discovered that the sensitivity is enhanced compared to atmospheric operation over a range of outlet pressures from approximately 200 to 400 torr; however, operation of the FID at the lowest possible pressures decreases the analytical sensitivity due to both the outlet pressure and the absence of helium makeup gas. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 226–235, 2000