Supply System, High Pressure Pump and Controller

The SF purity is a very important parameter in SFE (i.e., supercritical CO2 purity is 99.9999%). The high purity is required for analytical extractions since if a universal detector is being used nonvolatile impurities in the CO2 become trapped along with the separated analytes and these impurities may interfere with the analyte assay. 

Usually, the gas supply system is simply a laboratory-sized cylinder. However, for applications where pure SF CO2 is inadequate, mixtures of fluids may be used. Mixtures of fluids may be made in two different ways (i) premixed fluids may be directly supplied in one unique cylinder or (ii) both fluids are supplied in separate cylinders and mixed before the pump, where the mixture is pressurized to the desired value. 

During the entire extraction process the fluid must be pumped at a constant pressure from the container to the extractor cell. Two major pump types are found in SFE instruments syringe and piston. Nowadays, it appears that the majority of SFE instmments incorporate piston pumps. An auxiliary pump may be necessary when modifiers are used. Some manufacturers provide two pumps (usually as an option) with one delivering the primary fluid and the other delivering the desired level of cosolvent. 

The majority of SFs are highly compressive, so pressure control must be adequate. Many SFE instruments control several gradients of CO2 pressure. Also, fluid flows must be reproducible. 

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Supply System, High Pressure Pump and Controller... 

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