1. T. S. Ma and R. Rittner, Modem Organic Elemental Analysis, New York: Dekker. 1979.
2. G. Ingram, Methods of Organic Elemental Analysis, London: Chapman & Hall. 1962. p. 465.
3. F. Armstrong in H. Halmann (ed.), Analytical Chemistry of Phosphorus Compounds, New York: Wiley. 1972. p. 748.
4. W. Rieman and J. Beukenkamp in I. Kolthoff and P. Elving (ed.), Treatise on Analytical Chemistry, Part II, Vol. 5. New York: Interscience. 1961. p. 348.
5. W. Awad, S. S. M. Hassan, and S. Thoria, Mikrochim. Acta [Wien]1976 II, 111.