High-Performance Liquid Chromatography (HPLC) Measurement of Rebamipide. COR was determined by amodification of Shioya’s HPLC method (12) as follows: biopsy specimens and gastric mucus were added to 1.0 ml of distilled water and homogenized in a polytron. To 0.2 ml of homogenate or serum, internal standard methanol solution (OPC-12823, 200 ng/ml) was added, and the mixture was stirred and allowed to stand for 30 min. To this mixture was added 0.2 ml of distilled water. The new mixture was stirred and centrifuged at 9500g for 5 min. The supernatant was filtered through a 0.45-m membrane filter, and 150 l of the filtrate was injected into the HPLC system as the sample solution.