Rapid estimation of theoretical counter-current distribution values.

The usefulness of the Craig counter-current distribution technique (1, 2) for studying the purity of compounds and the metabolic fate of therapeutic agents can be augmented by deriving the theoretical distribution values from the “Tables of the binomial probability distribution” (3). By use of such tables, which only recently have become generally available, laborious calculation of theoretical counter-current values can be reduced to a minimum. Thus, the plotting of theoretical distribution curves for any number of transfers in the manner described by Williamson and Craig (4) is greatly facilitated. As proposed by Williamson and Craig (4), the fraction of a solute present in a given tube on completion of the fundamental procedure can be calculated by expanding the binomial