John, P.; Azeem, W.; Ashfaq, M.; U. Khan, I.; N. Razzaq, S.; Ud-Din Khan, S. Stability-Indicating RP-HPLC Method for Simultaneous Determination of Methoxsalen and P-Aminobenzoic Acid in Binary Combination. Bull. Chem. Soc. Eth. 2015, 29, 27-39.