Evaluation of selected filters for collection and subsequent supercritical fluid extraction of suspended solids for trace organic analysis

This study evaluated selected filters in order to find an appropriate filter that can be used to separate suspended solids (SS) from the aqueous phase with minimal sorption of the dissolved organic constituents in the aqueous phase, and that is compatible with subsequent supercritical fluid extraction (SFE) of hydrophobic organic compounds (HOCs) from the SS collected onto them. The sorption study for the filters was limited to the use of analytes in aqueous solution with no SS. Membrane filters and a glass-fiber filter with binder showed considerable sorption behaviour during filtration of aqueous solutions consisting of six polynuclear aromatic hydrocarbons (PAHs) as analytes. The extent of sorption of the analytes by the filters increased with the more hydrophobic compounds. A glass-fiber filter with no binder (MSI TCLP) was found to be non-sorbing towards the PAH analytes, and was further shown to be an appropriate fitter for a series of 56 base/neutral/acid extractable organic compounds. SFE of the filter as received showed extractable compounds detectable by GC-MS. Thus, pre-cleaning of the filter is required for the removal of SFE-extractable background compounds prior to its use in the collection of SS for subsequent SFE.