Trihexyphenidyl hydrochloride

Deionized and distilled water, purified using a PURELAB flex system (ELGA, Marlow, UK), was used to prepare all aqueous solutions. Ibuprofen, propranolol hydrochloride and trihexyphenidyl hydrochloride were obtained from Sigma-Aldrich (St. Louis, MO, USA). (±)-2-(6-Methoxy-2-naphthyl) propionic acid [(±)-naproxen], ketoprofen, pindolol, propafenone hydrochloride, chlorpheniramine maleate, warfarin, verapamil hydrochloride, and ammonium formate were purchased from Wako Pure Chemical (Osaka, Japan). (R,S)-Loxoprofen was kindly donated by Daiichi-Sankyo Co Ltd. (Tokyo, Japan). HPLC-grade acetonitrile (MeCN) and ethyl acetate were obtained from Kanto Chemicals (Tokyo, Japan). All other chemicals were used as received in the highest purity available. Each stock solution of chiral pharmaceuticals (10 mmol/L) except for NSAIDs (Ibuprofen, loxoprofen, naproxen, ketoprofen) was prepared in water. Stock solutions of the NSAIDs (10 mmol/L) were prepared in methanol. These solutions were stored at 4°C and diluted with water to the desired concentration immediately before use. The pH (3.0, 4.6, 6.0) of 10 mmol/L aqueous ammonium formate solution used in mobile phase was adjusted by the addition of 1 mol/L hydrochloric acid.