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

Abstract

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 (30:70) adjusted to pH 4.0 with NaOH gave optimum phase capacity ratios of -0.21 for I-, 0.93 for IHA and 1.54 for IBA. On the chromatograph used, 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 (1 mg/100 ml) in the eluent. The recoveries of 123I-123IHA and 123IBA from the column were found to be 100.6% (s.d. 1.3), 100.2% (s.d. 2.1) and 98.1% (s.d. 1.2) respectively (n = 10 for each compound). 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% (+/- 0.2 s.e.) by h.p.l.c. and 98.3% (+/- 0.2 s.e.) by t.l.c. This difference was found to be significant (P less than 0.05) and an explanation for this difference is proposed. A coefficient of variation of 0.1% on the results from the repeated analysis (n = 20) of one preparation of [123I]IHA, demonstrated that the h.p.l.c. method was capable of very high precision.