Electron spin resonance identification of irradiated ascorbic acid: Dosimetry and influence of powder fineness

Abstract

As an alternative to heat and gas exposure sterilization, ionizing radiation is gaining interest for sterilization of medicinal products. Detection and dosimetry of pharmaceuticals radiosterilization is a growing concern to numerous regulatory agencies worldwide; in this context, in the absence of suitable analytical methods, our attention was focused on electron spin resonance (ESR) spectrometry. This paper reports experimental data on the ESR identification of irradiated ascorbic acid and sodium ascorbate; also described are some data on powder fineness dependence in ESR dosimetry. While the ESR spectra of non-irradiated samples present no intensity, a signal, dependent on the irradiation dose, is found in irradiated samples. However, preliminary to the study, care was taken with the use of microwave power to avoid power saturation. The number of free radicals was estimated by comparison of the second integral from radiosterilized samples and diphenylpicrylhydrazyl standard; the values were in the range 1.5×10 19–3.4×10 19 radicals mol −1 ( G from 0.05 to 0.12). Aside from qualitative detection, ESR spectrometry can be used for dose estimation. When an exponential function is applied to the variation of peak to peak amplitude vs. dose the function correlates well with the data. Free radical evolution vs. storage time was modelled using bi-exponential function. From this, the time limit from the irradiation (25 kGy) for identification of irradiated vitamins by ESR were evaluated. In commercially marketed drugs, radicals should be detectable up to two years after irradiation; this will probably be the case for the four samples (three samples of ascorbic acid of different powder fineness and one sample of sodium ascorbate) studied.