A sensitive and reproducible high-performance liquid chromatography-fluorescence method was developed and validated for quantitative determination of indoxyl sulfate in plasma using methyl paraben as an internal standard. The separation was carried out on an OSD-2 C18 Spherisorb column by isocratic elusion with sodium acetate buffer (pH 4.5) and acetonitrile (10:90, v/v) as the mobile phase. The method was validated and found to be linear in the range of 2.5 to 50 µM. The limit of quantification was 2.0 µM. The variations for intra-day and inter-day precision were less than 10.1%, and the accuracy values were between 93.4 and 102.5%. The extraction recoveries were more than 89%.
