DSC and EPR analysis of some radiation sterilized alkaloids

Abstract The effect of ionising radiation on the physico-chemical properties of salts of three alkaloids has been studied: codeine phosphate (COD), papaverine hydrochlo-ride (PAP) and pilocarpine hydrochloride (PIL). These compounds in the solid state were irradiated with an e-beam of the energy of 9.96 MeV to achieve doses ranging from 25 to 400 kGy, and then they were subjected to organoleptic analysis, thermal analysis (differential scanning calorime-try, DSC), electron resonance (EPR) spectroscopy, scan-ning electron microscopy observations and X-ray diffraction study. The most informative were the results provided by the EPR and DSC methods. The EPR spectra revealed the presence of long-lived radicals whose con-centration was directly proportional to the dose of irradia-tion for all the compounds studied. (PIL 2.14 9 1016 spin/g, COD 6.85 9 1015 spin/g, PAP 2.50 9 1014 spin/g—for the dose of 100 kGy). The DSC results revealed a decrease in the melting point by 5.9 C for COD and by 0.8 C for PIL after irradiation with 200 kGy, which is indicative of products of radiolysis, of which at least one is non-white, and changes the colour of the compounds. PAP, for which no decrease in the melting point and no colour change was observed and for which the concentration of free radicals was the lowest, was found to be most stable from among the compounds studied. It will probably be suitable for radia-tion sterilisation. The other two compounds COD and PIL show much lower radiochemical stability and should be subjected to more detailed examination to establish the mechanism of radiolysis and the possibility of radiation sterilisation. Our results have confirmed the earlier reports on high radiochemical stability of PAP, but do not confirm the resistance to ionising radiation of COD and PIL