1. T. S. Ma and M. Gutterson, Analyt. Chemistry50, 86R (1978).
2. G. Ingram, Methods of Organic Elemental Microanalysis, London: Chapman & Hall. 1962.
3. J. Alicino, A. Cohen, and M. Everhard, in I. Kolthoff and P. Elving (eds.), Treatise on Analytical Chemistry, Part II, New York: Interscience. 1965. p. 57.
4. C. Wilson and D. Wilson, Comprehensive Analytical Chemistry, Vol. IB, Amsterdam: Elsevier. 1960.
5. W. Selig, Mikrochim. Acta [Wien]1970, 168.