A nondestructive technique to determine the rate of oxygen permeation into solid dosage forms.

The current study investigated the use of electron paramagnetic resonance (EPR) spectroscopy as a nondestructive method to quantify the partial pressure of oxygen (PO2) in tablets and hard shell capsules. Lithium phthalocyanine crystals (LiPC) were placed inside the dosage forms. The peak-to-peak linewidth of the first derivative of the LiPC EPR spectra was measured and, by calibration tables, the oxygen partial pressure, pO2, within the dosage form was determined. The intra-dosage form pO2 was followed as a function of time after changing the exterior gas stream composition. Results showed initial oxygen concentrations comparable to atmospheric levels in all tablets and capsules investigated. Oxygen rapidly permeated into unsealed gelatin and cellulosic hard shell capsules. Banding at the cap/body joint significantly reduced the oxygen permeation rate. Oxygen also rapidly permeated into tablet compacts, regardless of the compressional force used during tableting, while application of a polymeric film significantly decreased the rate of oxygen permeation. This EPR technique was shown to be a suitable nondestructive method to study oxygen permeation kinetics in solid dosage forms.