A high performance liquid chromatographic method for determination of the radiochemical purity of iodohippuric acid [123I] injection

A method for the separation of the radiopharmaceutical iodohippuric acid ([123I]IHA) from the two impurities produced in the labelling reaction, iodide (123I-) and iodobenzoic acid ([123I]IBA) has been developed using reversed-phase high performance liquid chromatography (h.p.l.c.). The effect of eluent pH on the separation of the three compounds was studied. An eluent consisting of methanol:0.1 M acetic acid adjusted to pH 4.0 gave optimum phase capacity ratios of -0.21 for I-, 0.93 for IHA and 1.54 for IBA. This corresponded to an analysis time of 4 min per sample. To recover 123I- from the column with a good peak shape, it was found necessary to include sodium iodide in the eluent. The recoveries of 123I- 123IHA and 123IBA from the column were found to be 100.6%, 100.2% and 98.1% respectively. H.p.l.c. was compared with the standard thin layer chromatographic (t.l.c.) method of analysis on 10 preparations of [123I]IHA which gave a mean radiochemical purity of 99.1% by h.p.l.c. and 98.3% by t.l.c. This difference was found to be significant and an explanation for this difference is proposed. A coefficient of variation of 0.1% on the results from the repeated analysis of one preparation of [123I]IHA, demonstrated that the h.p.l.c. method was capable of very high precision. (author)