Registered Pharmacist S.K.R.I.Medicines Centre, Rajkot, Gujarat, India,
M.Pharm Semester-I Student of B.K.Mody Govt.Pharmacy College Rajkot,
Department of Pharmaceutics GTU, Gujarat, India.
Spectrophotometry is an attractive method for PKa determination in very diluted aqueous solution about 10-5 to 10-6M provided that the compound possesses PH dependent light absorption due to the presence of a chromospheres in proximity to the ionization centers. Traditionally 6 to 8 aliquot solutions of samples in identical concentrations but with different PH values are prepared & their absorption spectra are registered at single wavelength. This series of solutions can be generated by either preparing the sample in buffer solutions of known PH or titrating the sample solution e.g. alkalimetry. Then half the absorbance of maximum plotted on graph & interpolated on x-axis that will give value of PH is Pka & negative Antilog of that value at base 10 give value of ka i.e. Dissociation Constant (Pka=-logka). This exercise is carrying out in below assignment.