Indoxyl sulfate is one of the most extensively studied solutes that accumulates in the plasma when the kidneys fail. Originally called "indican", it was first isolated by Obermayer and Popper in 1911. High concentrations of indoxyl sulfate in blood plasma are known to be associated with the development and progression of a number of pathological conditions including chronic kidney disease and vascular disease. The scientific literature documents the use of older generation C18 columns, using type A silicas. This application brief will illustrate the application of a new generation C18 column, based on type B silica, for the analysis of indoxyl sulfate, Figure 1, as part of a research study to measure the total levels in a simulated blood serum environment.