PRESSURE-REGULATING FLUID INTERFACE AND PHASE-BEHAVIOR CONSIDERATIONSIN THE COUPLING OF PACKED-COLUMN SUPERCRITICAL-FLUID CHROMATOGRAPHY WITH LOW-PRESSURE DETECTORS

Packed-column supercritical fluid chromatography is usually performed with flow control on the upstream side of the column and pressure cont rol on the downstream side. This arrangement is compatible with detect ors that can be operated at column-outlet pressure and placed between the column outlet and a pressure-regulating device. However, mass tran sfer problems may arise when low-pressure detectors like a mass spectr ometer or evaporative-light-scattering detector are used with downstre am pressure regulators or programmable nozzles. These problems can be avoided by replacing the regulator or nozzle with a tee delivering a p ressure-regulating make-up fluid from a pressure-controlled pump. Para meters are chosen to avoid the liquid-vapor two-phase regions of the p hase diagram for the resulting mixture. We demonstrate this approach a nd show how to use phase diagrams and their pressure-temperature proje ctions for setting operating conditions. (C) 1998 Elsevier Science B.V . All rights reserved.