Quinine Actinometry as a Method for Calibrating Ultraviolet Radiation Intensity in Light-Stability Testing of Pharmaceuticals

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Abstract
A collaborative study was carried out by seven different laboratories to evaluate quinine actinometry as a universal, standardized method for calibrating UV radiation intensity from light sources used in light-stability testing of pharmaceutical products. Near UV fluorescent lamps, white fluorescent lamps, metal halide lamps and xenon arc lamps were employed as light sources. The increase in absorbance at 400 nm of aqueous quinine solutions was found to be proportional to the integrated UV energy emitted from the light sources. The linearity observed between absorbance and integrated UV energy indictates that quinine actinometry can be used to measure the intensity of UV radiation at wavelengths around 330 nm. The slopes of regression curves of absorbance vs integrated UV energy varied among the lamps used due to differing spectral distributions. Light degradation of nifedipine, a model photosensitive drug, was studied based on quinine actinometry.