The influence of pH on losses of analyte estradiol in sample pre-filtration

Abstract

Cellulose acetate 0.45-μm syringe filters could be used to filter environmental samples containing steroidal hormones, such as estradiol, prior to analysis. Such pretreatment may result in significant loss of analyte due to either adsorption of analyte to the filter material or association with retained colloidal and particulate materials. To determine the quantity of such losses, several experiments were performed by filtering water spiked with estradiol at different concentrations (50, 100, and 500ng/L) and pH (3–12) through cellulose acetate syringe filters. Further, the influence of added organic matter was studied. At all concentrations the experiments indicated that below pH 11, up to 50% of estradiol in the feed was adsorbed on the filter. This occurred regardless of the presence of bulk organic matter in solution, and was related to dissociation of estradiol with pH and subsequent changes in filter interaction. As a consequence, pretreatment of solutions containing estradiol should be adjusted to greater than pH 11 prior to filtration with 0.45-μm cellulose acetate filters.