Determination of orotic and dihydroorotic acids in biological fluids and tissues.

In commonly used procedures for colorimetric assay of orotic acid in biological materials, certain substances interfere, positively or negatively. Some that interfere negatively are ornithine, cysteine, citrulline, tyrosine, proline, hydroxyproline, and polyamines. Protein and interfering agents are easily removed by first isolating the total organic acid fraction. The orotic acid in this fraction can then be determined by an established colorimetric procedure. A rapid liquid-liquid column-chromatographic procedure is described, if analysis of both dihydroorotic and orotic acid is required.