[Study on the interaction between alginic sodium diester and azur A and the application].

The interaction of alginic sodium diester (ASD) and azur A (AA) was studied by absorption spectra. The influence of pH and the molar ratio of AA/ASD on the spectra was investigated. The maximum binding number (N = 168) and the binding equilibrium constant (K = 3.25 x 10(6)) of the alginic sodium diester and azur A were obtained by the theoretical model. The new method for the determination of ASD was developed by the formation of ASD-AA ion-association complex that caused the fading of the AA. The detection limit is 0.009 microg x mL(-1). The method has the advantages of simplicity, stable system, good accuracy and selectivity, and was applied to the determination of alginic sodium diester in tablets with satisfactory results.