Analytical Supercritical Fluid Extraction of Lipid Containing Samples

Abstract: Traditionally, sample work-up has been associated with different kinds of liquid extraction techniques involving a large consumption of hazardous solvents. There are today regulations that aims at replacement of dangerous chemicals which has created a need for new extraction techniques. During the last decade supercritical fluid extraction (SFE) has become a good alternative for sample pretreatment in analytical chemistry. The technique can be used for virtually all kinds of matrices and analytes with exception for the most polar ones. SFE offers a high degree of selectivity and can be used to fractionate analytes and different matrix components by choosing proper extraction conditions. To further increase the selectivity, active adsorbents can be added to the sample. For lipid rich samples this approach offers fat free time windows allowing a selective extraction of non-polar analytes as PCBs. The extracts can be analyzed without any further pre-treatment. It has also been shown that modifiers can be used, but an excessive use can destroy the retaining capability of the adsorbents. Furthermore, utilizing solid phase trapping can also enhance the selectivity. The analytes are recovered by rinsing the trap with a suitable solvent. Here the choice of packing material and rinse solvent is important. For large volumes of fluid samples, a new design of the extraction cells has been developed. Here, the sample is enclosed between two porous membranes, which prevents leakage during sample loading and after the extraction. With this approach slightly modified standard extraction cells can be used. With supercritical fluid chromatography (SFC) it is possible to get information about the amount co extracted fat in SFE extracts. SFC offers the possibility to use detection techniques used for both liquid chromatography and gas chromatography. In combination with high selectivity, speed, and limited need for derivatization, SFC is a good alternative to conventional analytical methods.