Abstract
Solubilization of drugs with surfactants often causes changes of the absorbance and the maximum absorption wavelength. In this study, it was found that the shifts of the absorption maxima of alkylparabens depended on the concentration of the surfactant, sodium dodecyl sulfate, but not on the concentration of the drugs. The first derivative absorption spectrum was used to evaluate the wavelength shift.The distribution parameter is defined as the ratio of the amount of the drug in the micellar phase (calculated from the absorption shift-length) divided by the amount of surfactant in the micellar phase to the amount of the drug in the bulk phase divided by the amount of surfactant in the bluk phase. This distribution parameter differs from the partition coefficient. It was found that the longer the alkyl chain length of the alkylparabens, the greater the absorption shift-length and the distribution parameter. Alkylparabens are very difficult to differentiate from each other in terms of the absorption spectra, but can easily be distinguished by using the distribution parameter. This approach may be generally useful for distinguishing drug homologs.
