Study of protonation equilibrium of lorazepam by potentiometry and multiwavelengths spectrophotometry

The acid-base equilibrium of lorazepam was studied by means of potentiometry and multiwavelengths spectrophotometry. The stoichiometric equilibrium constants were determined at 25 °C and constant ionic strength 0.1 mol L-1 (NaCl). The acidity constants pK1=1.58±0.05 and pK2=11.67±0.07 were found by potentiometry, and pK1=1.54±0.02 and pK2=11.61±0.03 by multi-wavelengths spectrophotometry. Potentiometric determination of equilibrium constants was performed by application of the formation function method. Data analysis program applied for multi-wavelengths spectrophotometric determination of acidity constants.