High-speed, thermally modulated SFE/GC for the analysis of volatile organic compounds in solid matrices

A coupled supercritical fluid extraction (SFE) and high-speed gas chromatography (GC) system was developed which permits simultaneous sample extraction and analysis. A thermal desorption modulator at the head of a 50-μm i.d. capillary column was used as an interface between the SFE and GC. The extraction fluid was first split between the modulator and a waste collection vessel. The substances introduced into the modulator were concentrated in the stationary phase and then released as a sharp injection pulse to the analytical column by electrical resistance heated thermal desorption. The modulator was operated at 10-s time intervals, which generated consecutive concentration pulses to the column. These concentration pulses were separated into individual chromatograms by high-speed GC. A set of chromatograms could be generated while the extraction proceeded. With this system, the extractant was sampled continuously so that the SFE process could be monitored in real time for selected components. Quantitative results could be extrapolated before extraction was complete from curves obtained by signal averaging of segmented chromatograms from the set.