Ultramicromethod for determination of plasma uric acid.

We describe an ultramicromethod for determination of uric acid by a manual procedure. Hydrogen peroxide, formed when uric acid is oxidized in the presence of uricase, oxidatively couples two molecules of p-hydroxyphenylacetic acid in the presence of peroxidase to produce a highly fluorescent compound. The specificity of the uricase reaction is retained, and the fluorometry results in a higher sensitivity (but a lower precision) than that obtained by applying spectrophotometric methods. As little as 50 ng of uric acid can be determined, and only 10 mul of plasma is required. Values obtained for human plasma are higher than those obtained by the spectrophotometric method.