Multivariate optimization of supercritical fluid derivatization and extraction of phenol in soil samples

Two-level (Packett-Burman) and three-level (central composite) orthogonal factor designs are used as a formal optimization procedure for the supercritical fluid derivatization-extraction of phenol in soil samples by acetylation. Nine variables are considered: carbon dioxide flow rate, fluid density, extraction cell temperature, static extraction time, nozzle and trap temperatures, amount of derivatizing reagent, pyridine concentration, and time of contact between the derivatizing reagents and sample prior to extraction. The dynamic extraction process is carried out in four steps to simultaneously study the extraction kinetics of the process. The results suggest that only the extraction cell temperature and the amount of derivatizing reagent used are statistically significant to the overall extraction yield, as is the extractant flow rate to the kinetics. The procedure is validated by processing a certified reference material; special attention is paid to developing a test material for this type of experiment.