Application of the Wagner-Nelson absorption method to the two-compartment open model

Abstract

This report considers the application of the Wagner- Nelson method to both one- and two- compartment open model data when there is no competing reaction at the absorption site. Equations are derived which show that application of the Wagner- Nelson method to data which obey the twocompartment open model with first-order absorption allows accurate estimation of not only the rate constant ka but also the parameters of the two- compartment open model, namely k12, k21, and kel. In the example given, this new method was more accurate than the classical “feathering” or ”back- projection” method. The appropriate criterion for “collapsing” the two- to the onecompartment open model is given. In cases where the one-compartment open model applies, and absorption is first order but abruptly ceases after some time, it is shown that ka may be accurately estimated by application of the Guggenheim method to the AT/V values calculated for the absorption phase.