Liquid chromatography recycling system

Furthermore, although most of the CO2 is recycled from the gas-liquid separators, a substanhal amount of dissolved CO2 remains in the co-solvent recovered, which flashes away and is lost during the final product recovery. Therefore, CO2 losses in large-scale SFC systems often lead to higher production costs than those in liquid chromatography systems equipped with appropriate solvent recovery units, as discussed in the next section. 

Since ISEs can be used in continuous flow systems or in flow systems with sample injection (flow injection analysis, FIA)21 their application is wide, not limited to discrete samples. Analysis time becomes shorter, with faster recycling. Additionally, in flow systems the experimental assembly and data analysis can be controlled automatically by microcomputer, including periodic calibration. Another development is the use of sensors for the detection of eluents of chromatographic columns in high-pressure liquid chromatography (HPLC). Miniaturization has permitted an increase in the use of sensors in foods, biological tissues, and clinical analyses in general. 

At the inlet of the main pump, CO2 is in liquid state (40 bars and —5 °C), and at the outlet of the pump, CO2 is at the operating pressure. After heating, CO2 is in supercritical state, ready to be used for chromatography. At the outlet of the column, a decompression turns the mobile phase to a biphasic system gaseous CO2 and droplets of solute. Separators allow the recovery not only of the solute, but also of gaseous CO2 that can be recycled after cooling. At the end of this process, the CO2 makes a complete turn around its critical point. 

The performance of several column packings has been assessed and it has been stressed that low eluent flow rates are necessary for high performance separation. The effects of water contamination in eluents has been studied by Berek et a/. " highlighting the need for rigorou dried systems. Phase equilibria studies in polymer-polymer-solvent systems have proved feasible using a dual detection system and could be extended in the future. Other applications are concerned with copolymer analysis, polydispersity, oligomers, and melamine-formaldehyde and urea— and phenol-formaldehyde resins. New techniques, recycle liquid SEC, phase-distribution chromatography, and the measurement of diffusion coefficients from GPC have been described. 

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