AUTOMATED MEASUREMENT OF SPECIFIC ACTIVITY OF RADIOLABELED LIGANDS DURING SYNTHESIS

摘要

Accurate determination of specific activity is vital to the analysis of PET imaging data for saturable processes where unlabeled ligand will compete with the radioligand at the target receptor, transporter or enzyme. Accordingly, it would be helpful to know specific activity of the tracer prior to administration of the dose. This is particularly difficult for nC-tracers due to the short physical half-life and the time required to analyze an aliquot of the final formulation. While it is easy to measure the radioactivity concentration (Ci/mL) of the injectate, it can be problematic to measure the low chemical concentration (_ mumol/mL) of the diluted analyte. For low yield reactions, it is often difficult to reserve sufficient volume of final product to perform all required quality control analyses. Also, chemical instability of the ligand can lead to over-estimation of specific activity when using delayed measurements. We present a method for simultaneously measuring the total radioactivity and mass of the labeled compound as it elutes from the semi-prep HPLC column. In this manner, specific activity can be rapidly calculated irrespective of the amount of tracer which might be lost during solvent evaporation, recovery and product formulation.