Radiochemical purity and in vitro stability of commercial hippurans

Good radiochemical purity of hippuran is important regarding the patient's radiation dose, primarily because of the high thyroid exposure from free iodide. The radiochemical purity and in vitro stability of 11 commercially available 131I, 125I, and 123I hippurans were analyzed by means of thin layer chromatography. Three different radioactive impurities were found in all hippuran samples: (a) free radioiodide, (b) a radiochemical impurity that has been unknown up until now, and (c) labeled o-iodobenzoic acid. Quality control of several hippurans with regard to radiochemical purity gave evidence of considerable differences during storage. The lowest amount of free-iodide was 0-0.6% in a hippuran preparation from one manufacturer, the highest amount 0.8-4.6% in a sample from another manufacturer. Hippuran samples from four other manufacturers were found to contain greater than 2% of free iodide prior to their expiration date.