An approach for monitoring subcritical water extraction kinetics of fluorescent analytes

The coupling of an extractor, which enables water at temperatures up to 300 °C to be used, and a continuous manifold, which incorporates a fluorimetric flow-cell packed with a C18 solid support for simultaneous retention and detection, constitutes a valid approach for continuous monitoring of leaching kinetics. The performance of this assembly has been checked using solid matrices such as diatomaceous earth and silica gel which have been spiked with pyrene. The fluid from the extraction chamber is cooled and driven to the spectrofluorimeter where the fluorescent analyte is retained. A rising curve is obtained as the concentration of pyrene on the C18 support increases, which evolves to a plateau indicative of the completion of the leaching process. The influence of variables such as temperature, pressure and flow-rate of the leaching agent and type of matrix spiked with pyrene on the extraction kinetics is shown by the shape of the integrated retention-detection curves. The approach can be applied not only to fluorescent and coloured analytes, but also to species which yield such products with reagents contained in the leaching agent or which are mixed with it along the continuous manifold.