Polychromatic-Light Irradiation Kinetics of Dacarbazine and Nifedipine. Application as New Reliable UVA-drug-actinometers.

The photokinetic behaviour of materials driven by polychromatic light is an area that has not received a lot of attention in the literature. Most often, such photokinetic data is treated by thermal kinetic models (i.e., the classical 0th -, 1st - or 2nd -order equations). Such models were not analytically derived from the rate-laws of the photodegradation reactions. Polychromatic light kinetic modelling is hence of importance, as a means to providing adequate toolkits and metrics. This paper aims at proposing two reliable drug-actinometers useful for polychromatic UVA range. The general actinometric methodology offered here is also useful for any drugs/materials obeying a primary photoprocess where both reactant and photoproduct absorb the incident light, of the \(AB{\left(1{\Phi }\right)}_{{\epsilon }_{B}\ne 0}\) type. The present method has been consolidated by the η-order kinetics, a mathematical model analytically derived from the photosystem’s rate-law. This represents the first ever equation in the literature, to model polychromatic light of this reactive system. This framework further demonstrated the lamp-specificity of actinometers. Overall, Dacarbazine and Nifedipine photodegradations obeyed η-order kinetics, and stand as effective actinometers that can be recommended for the ICH Q1b photostability testing.