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2. British Pharmacopoeia, HMSO, 1988, London, p. 392.
3. The United States Pharmacopoeia, 20th revision. U.S.P. Convention, Inc. 12601, 1980, p. 551.
4. J. L. Fabregas, E. Casassas,Anal. Chim. Acta 1979,107, 401.
5. Y. K. Agarwal, D. R. Patel,Anal. Lett. 1986,19, 1289.