ESR spectroscopy applied to the study of pharmaceuticals radiosterilization: cefoperazone

As an alternative to heat and gas exposure sterilization, ionizing radiation is gaining interest as a sterilization process for medicinal products. Nevertheless, essentially for economic profits, an unauthorized and uncontrolled use of radiation process may be expected. In this context, it is necessary to find methods distinguishing between irradiated and unirradiated pharmaceuticals and, in the absence of suitable detection methods, our attention was focused on ESR spectrometry. In this paper, we examine the potential of ESR as an analytical tool in cefoperazone radiosterilization; this cephalosporin is a potential candidate for radiation treatment due to its thermosensitivity. While the ESR spectra of unirradiated sample present no intensity, a signal, dependent of the irradiation dose, is found exclusively in irradiated samples. The number of free radicals (2 x 10(17) radicals per g at 25 kGy) was estimated by comparison of the second integral from radiosterilized samples and DPPH. From this, the G-value could be estimated to 0.3. Limit of detection and limit of quantification are 0.5 kGy and 1 kGy, respectively. Aside from qualitative detection, ESR can be used for dose estimation. The dose-ESR response curves can be simulated by bi-exponential or power functions and the linear function can't be used for simulation even for low doses. Decay of radicals upon storage were simulated using bi-exponential function. The limit of detection of free radicals after irradiation at 25 kGy is 140 days.