Spectrophotometric Determination of Aciclovir with Thymol Blue and Its Reaction Mechanism

In a phosphate buffer medium of pH 7.84,an ion association complex was formed between aciclovir (ACV) and thymol blue (TMB) with its positive absorption maxima at 596 nm,and negative absorption maxima at 436 nm.Linear relationships were obtained at both absorption maxima,and Beer′s law was held in the range of 2.05×10-6 to 2.38×10-5mol·L-1 of ACV at 596 nm,with an apparent molar absorptivity (ε596) of 3.19×104L·mol-1·cm-1,and a detective limit of 6.21×10-7mol·L-1.By applying the dual-wavelength measurement with wavelength addition method,the molar absorptivity was increased to 4.46×104L·mol-1·cm-1 and a lower detection limit of 5.13×10-7mol·L-1 was obtained.Most of the commonly coexisting ions and substances were found not interfering.In the analysis of some a ciclovir drugs,and the RSD′s (n=6) calculated were in the range of 0.68%-2.76%.Results of recovery test obtained were in the range of 99.1%-103.3%.Reaction mechanism of the formation of ion association complex between ACV and TMB was studied and it was shown that the ion-association complex was formed not only due to electrostatic action,but also to charge transferring and to the van der waals force and the hydrophobic action.