There are five main types of experimental data that are used for the determination of solution equilibrium constants. Potentiometric data obtained with a glass electrode are the most widely used with aqueous solutions. The others are Spectrophotometric, Fluorescence (luminescence) measurements and NMR chemical shift measurements; simultaneous measurement of K and ΔH for 1:1 adducts in biological systems is routinely carried out using Isothermal Titration Calorimetry.
The experimental data will comprise a set of data points. At the ith data point, the analytical concentrations of the reactants, T, T etc. will be experimentally known quantities and there will be one or more measured quantities, y', that depend in some way on the analytical concentrations and equilibrium constants. A general computational procedure has three main components.
# Definition of a chemical model of the equilibria. The model consists of a list of reagents, A, B, etc. and the complexes formed from them, with stoichiometries AB... Known or estimated values of the equilibrium constants for the formation of all complexes must be supplied.
# Calculation of the concentrations of all the chemical species in each solution. The free concentrations are calculated by solving the equations of mass-balance, and the concentrations of the complexes are calculated using the equilibrium constant definitions. A quantity corresponding to the observed quantity can then be calculated using physical principles such as the Nernst potential or Beer-Lambert law which relate the calculated quantity to the concentrations of the species.
# Refinement of the equilibrium constants. Usually a Non-linear least squares procedure is used. A weighted sum of squares, U, is minimized.  The weights, w and quantities y may be vectors. Values of the equilibrium constants are refined in an iterative procedure.