Spectrophotometric determination of pKa of vasicine

The current experiment describes the preliminary determination of pKa value of vasicine. A UV Spectrophotometer Shimadzu UV-1601 PC model was used to determine the pKa value of vasicine, a pyrralazo quinazoline alkaloid used as expectorant and bronchodilator drug. Analytical wavelength was chosen as which two species of the molecule differ greatly in their absorbance. Seven buffer solutions [7.4-8.6] were prepared containing 10 microM of the drug. The optical density of each buffer solution was measured at analytical wavelength 281 nm. A set of values was obtained and the pKa value for vasicine was found to be 8.1234 +/- 0.2 after the calculation