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The high flow rates that result after decompression make the trapping of analytes one of the more difficult aspects of a supercritical extraction. By elevation of the pressure on the collection vial, the flow may be reduced and trapping efficiency improved, considerably. The effects of different collection vial pressures were evaluated. The best results were obtained at 25 atm. With the collection vial at 25 atm, the trapping efficiencies of different solvents were then investigated. Also considered were the effects of solvent volume, extraction flow rate, collection solvent geometry, and restrictor temperature. For a 30 min extraction--with the restrictor line at 200 degrees C--quantitative recoveries were obtained with analytes as volatile as chlorobenzene (approximately 90%) in 1 mL of solvent. Mild precooling of the collection vessel allowed quantitative recoveries to be obtained down to benzene (94.2%).

High-performance liquid chromatography (HPLC) is the most versatile of the chromatographic techniques because it is applicable to a wide variety of analytes. Unfortunately, liquid mobile phases have relatively low diffusivities. A novel approach is presented for increasing the diffusivity of a liquid mobile phase. The method advocated in this study is the first process that has been described by which it is possible to increase the diffusivity of a liquid while having essentially no effect on other physical properties of the liquid, such as the temperature or solvating power. It is demonstrated that it is possible to sharpen peaks, in an HPLC separation, by the application of microwave radiation.

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Supercritical fluid extraction was directly coupled with gas chromatography such that the entire extraction effluent was directed onto the GC column. A sealed connection between the restrictor and the column ensured that no loss of analyte could occur. The elevated pressure generated in the column itself resulted in a reduced flow rate through the column, making efficient trapping possible. Metal-jacketed capillary columns were used as they can tolerate the elevated pressures required. In addition to maximizing sensitivity, very practical extraction parameters were possible. For a 25-min extraction, with a 2.2 mL/min flow rate, and the column at 40 degrees C, analytes as volatile as C-14 were trapped and separated. Trapping efficiency improved further with shorter extraction times, mild cooling of the column, or lower flow rates.