Optimization of a drying method for filtered suspended solids from natural waters for supercritical fluid extraction analysis of hydrophobic organic compounds

This paper describes a closed-jar drying method (with a desiccant), developed specifically for filtered suspended solids, as a more efficient alternative to air-drying or freeze-drying. Supercritical fluid extraction (SFE) recovery studies to evaluate its efficiency were achieved with hydrophobic organic compounds of log K-ow ranging from 3.9 to 5.2, represented by polynuclear aromatic hydrocarbons (PAHs). The PAH analytes were ''loaded'' onto the suspended solids by sorption to better represent field-collected material. The necessity of drying a sample of filtered suspended solids prior to SFE was confirmed by direct comparison of the SFE recoveries from dry and wet samples, These results indicate that the drying technique is needed to develop reproducible samples to analyze by SFE, An explanation for the effect of water in SFE is proposed. Optimization of SFE parameters for natural filtered suspended solids confirms that the best conditions for SFE of PAHs consist of a pressure of 355 arm, a temperature of 120 degrees C and a modifier consisting of 750 mu l of a 1:1:1 (v/v) mixture of water, methanol and methylene chloride.