An improved method of isomolar series for determining the composition
of an aqueous binary spectrophotometric system is proposed. It is base
d on the determination by dual-wavelength spectrophotometry of the equ
ilibrium concentration of the chromogenic agent L added in excess, the
absorbance of which has been found to be a linear function of n/m, th
e composition index of the reaction product M(m)L(n) in the system, He
nce it is a direct and reliable method, applicable also to systems in
which the absorption spectra of L and M(m)L(n) overlap and can be reso
lved by instrumental masking.