Abou-Dan, M., et al. “Conductometric Titration of Metformin in Pure Form and in Pharmaceutical Preparations Using Sodium Tetraphenylborate and Cetylpyridinium Bromide”. Asian Journal of Chemistry, vol. 13, no. 1, Mar. 2010, pp. 1-7, https://asianpubs.org/index.php/ajchem/article/view/22518.