Multiwavelength spectrophotometric resolution of the micro-equilibria of cetirizine

The acid-base properties of the antihistamine (HI receptor antagonist) ceti rizine have been studied by using a previously developed multiwavelength sp ectrophotometric titration method. A new computational procedure called "Tw o-Step-Divide-and-Conquer" (TSDC), which applied evolving factor analysis ( EFA) and target factor analysis (TFA), has been derived to unravel the micr o-equilibria of the triprotic zwitterionic compound from the spectral data. We have demonstrated that a single spectrophotometric titration experiment is sufficient to determine the 12 unknown microconstants and the distribut ion of microspecies, which are in good agreement with literature values, wh ere available.