ABSTRACTAn analytical methodology for the simultaneous determination of seven pharmaceuticals and two metabolites belonging to the non-steroidal anti-inflammatory drugs (NSAIDs) and analgesics therapeutic groups was developed based on off-line solid-phase extraction and ultra-high performance liquid chromatography coupled to tandem mass spectrometry 1 (SPE–UHPLC–MS/MS). Extraction conditions were optimized taking into account parameters like sorbent material, sample volume and sample 1,2 PH. Method detection limits (MDLs) ranging from 0.02 to 8.18 ng/L were obtained 2,3. This methodology was successfully applied to the determination of the selected pharmaceuticals in seawater samples of Atlantic Ocean in the Northern Portuguese coast. All the pharmaceuticals have been detected in the seawater samples, with pharmaceuticals like ibuprofen, acetaminophen, ketoprofen and the metabolite hydroxy ibuprofen being the most frequently detected at concentrations that can reach some hundreds of ng/L 4. Keywords: Non-steroidal Anti-inflammatory drugs (NSAIDs), Cyclooxygenase inhibitors, Prostaglandins, Aspirin.