An isothermal experiment with high pressure oxygen was established. The stability of 10% vitamin C solution as a model drug was studied and the kinetics parameters were obtained in a short time with the newly established experimental method. Because vitamin C degrades in both anaerobic and aerobic conditions, the total rate constant k_t can be expressed as: k_t＝k_an＋k_ae, where k_an and k_ae are the anaerobic and aerobic degradation rate constants, respectively. The k_an can be expressed as k_an＝A_an•exp(－E_a,an/RT) according to Arrhenius equation, and the k_ae was found to be k_ae＝A_ae•exp(－E_a,ae/RT)• in our experiments.

Key words: isothermal experiment with high pressure oxygen, drug stability, degradation kinetics, oxygen, vitamin C