OPTIMIZATION OF SUPERCRITICAL-FLUID EXTRACTION OF PHENOL AND CRESOLS IN SOIL SAMPLES

Two- and three-level factorial designs have been used to optimize the supercritical fluid extraction of underivatized phenol and cresols (o- , m- and p-cresol) in soil samples with a high content of carbon. An o verall eight variables [carbon dioxide flow-rate, fluid density, extra ction cell temperature, static extraction time, nozzle and trap temper atures, amount of methanol (as modifier) and the time of contact betwe en the added modifier and sample prior to extraction] were considered. The results suggest that thimble temperature and fluid density are st atistically significant factors to the overall extraction yield of the four analytes considered. Also, the static extraction time appears to be significant in the cases of m- and o-cresol. Special attention was paid to developing suitable test materials for this type of optimizat ion process. Moreover, validation of the extraction process was carrie d out by processing a certified reference material.