VARIABLE FLOW-CONTROL AND COLLECTION DEVICE FOR USE WITH SUPERCRITICAL FLUIDS

Real world samples which contain high concentrations of water and/or e xtractable material frequently cause intermittent or irreversible plug ging of the flow control device during off-line supercritical fluid ex traction (SFE). A supercritical fluid (SF) flow control/collection dev ice has been developed which can simultaneously maintain the extractio n flow-rate of the SF (+/-0.1 ml/min) and quantitatively (>90%) collec t analytes as volatile as n-octane directly into an organic solvent. W ith this device, the extract is partially depressurized through a heat ed capillary restrictor and into a pressurized collection solvent, so that both temperature and pressure are used to maintain the solubility of the extract in the SF. The pressurized mixture is finally depressu rized to atmospheric conditions using a backpressure regulator, so the extract can be recovered in the collection vial. Depending on the sam ple matrix, a restrictor heater temperature of 200 degrees C and a bac kpressure regulator with a heated (>5 wt% water in sample) or unheated (<5 wt% water in sample) exit tube is required to eliminate restricto r plugging. By varying the pressure of the collection solvent, a range of reversible and reproducible flow-rates were obtained at both high (400 bar, 3.5 to 0.2 ml/min liquid CO2) and low (100 bar, 0.8 to 0.1 m l/min CO2) SFE pressures using a 50 mu m I.D. capillary restrictor. At low (0.2 ml/min) SF flow-rates the solubility of several metal comple xes (e.g., ferrocene and Ni[C22H22N4] complex) was measured and reprod ucible solubility values and flow-rates (R.S.D.<8%) were obtained.