Pressurized liquid extraction of pharmaceuticals from sewage-sludge

A method for the quantitative determination of ten pharmaceuticals in sewage sludge was developed by using pressurized liquid extraction (PLE) and HPLC-MS with ESI (HPLC-(ESI)MS). The PLE was optimized with regard to solvents and operational parameters, such as temperature, pressure, extraction time, and purge time. The optimum conditions were: 50 mM phosphoric acid/methanol (1:1 v/v) as the extraction solvent, temperature of 100 degrees C, pressure of 100 bar, extraction time 15 min, 2 cycles, flush volume 150% and purge time 300 s. All recoveries for pharmaceuticals were over 68% except for salicylic acid. The repetitivity and reproducibility between days expressed as RSD was lower than 8% for repetitivity and 10% for reproducibility. The LOD of all compounds was lower than 10 microg/kg of dry weight of sewage sludge. The method was applied to determine the pharmaceuticals in sewage sludge from two domestic sewage treatment plants (STPs). The samples were collected every three months between February 2004 and June 2005. Some pharmaceuticals were determined in the samples and naproxen showed the highest value (242 microg/kg of dry weight).