Engalytcheff, A., Debuyst, R., Vanhaelewyn, G. C. A. M., Callens, F. J. and Tilquin, B. Attempts at Correlation of the Radiolytic Species of Irradiated Solid-State Captopril Studied by Multi-frequency EPR and HPLC. Radiat. Res. 162, 616– 622 (2004).

The purpose of this study was to provide insight into the processes that occur after the irradiation of solid-state drugs. Electron paramagnetic resonance (EPR) experiments were performed at two different frequencies, X-band (about 9.5 GHz) and Q-band (about 34 GHz), to identify the radicals present in irradiated captopril. The results confirmed that an irradiated drug can trap several main radicals. Moreover, the radical composition varied as a function of the treatment. In addition, non-volatile final products were studied by liquid chromatography coupled to UV and to mass spectrometry (LC-MS). The variation of the radical composition did not influence the profile of the final products; this appears to indicate that, in the case of captopril, the trapped radicals observed by EPR are not the main precursors of the final products. Finally, high-performance liquid chromatography data appear to indicate that radiosterilization of captopril is feasible.