A new method for the radiochemical purity measurement of 111In-pentetreotide

OBJECTIVES AND METHODSThe recommended method for the measurement of radiochemical purity (RCP) of In-labelled pentetreotide is thin-layer chromatography with a silica gel as the stationary phase and a 0.1 N sodium citrate solution (pH 5) as the mobile phase. According to the supplier’s instructions, the mobile phase must be prepared before the test is carried out, and the recommended stationary phase is off-market. We propose a new method for RCP measurement in which the mobile phase is acid citrate dextrose, solution A, which does not need to be prepared beforehand, and thin-layer chromatography is performed with a silica gel-impregnated glass fibre sheet as the stationary phase. We used both methods to measure the percentages of radiopharmaceutical and impurities. RESULTSThe range of RCP values obtained was 98.0–99.9% (mean=99.3%) by the standard method and 98.1–99.9% (mean=99.2%) by the new method. We observed no differences between the RCP values of both methods (P=0.070). CONCLUSIONThe proposed method is suitable for RCP testing because it yields results that are in good agreement with those of the standard method and because it is easier to perform as the mobile-phase solution need not be prepared in advance.