V. Venkatesh, A. Elphine Prabahar, P. Venkata Suresh, C. Uma Maheswari, and N. Rama Rao, “HPTLC Method for the Simultaneous Estimation of Etophylline and Theophylline in Tablet Dosage Form”, ajc, vol. 23, no. 1, pp. 309–311, Sep. 2010.