1. Satyanarayana K, Mishra RK (1974) Anal Chem 46:1609
2. Kolthoff IM (1937) Acid-base indicators. Academic Press, New York
3. Vogel AI (1985) Textbook of quantitative inorganic analysis, 4th ed, Longman, London
4. Standard methods for the examination of water and waste water, 14th ed (1975) American Public Health Association, Washington DC
5. Singh RB, Jain P, Garg BS, Singh RP (1979) Analyst 101:1187