Online coupling of supercritical fluid extraction sorbents chromatographic techniques

The objective of this study is to develop a technique for analysing atmospheric samples of volatile organic compounds that does not use solvent. This technique is based on coupling extraction using carbon dioxide (CO2) in a supercritical state to online analysis using conventional gas or liquid chromatography. At high pressure and at high temperature, matter can be brought to the supercritical state, between the gas state and the liquid state. The supercritical state gives fluids penetration and solubility properties that are far superior to those of usual liquid solvents. Extraction by using supercritical fluids is thus an extremely high-performance technique. Another advantage of this type of extraction is the ease of separation between the solvent and the solutes: mere expansion suffices to bring a supercritical fluid back to its gas state and to keep only the solutes in the liquid state.

Online coupling between such an effective extraction technique and conventional chromatography techniques should thus make it possible to consider analysing sample carriers without using solvent and without any intermediate handling. This offers two advantages: firstly protecting laboratory handlers from chemical risks, and secondly simplifying the analytical process that constitutes major part of the cost in risk assessment.

The main technical difficulty with this type of coupling lies in the interface between the extractor and the analysis instrument. It is on this point that efforts will be focused during this study, using both theoretical bases of supercritical fluid mechanics and thermodynamics and also recent developments made in this field for other applications.