Photometric method for determination of acidity constants through integral spectra analysis

• The method allows to obtain reliable values of acidity constants in 10–20 min.
• Only photocurrent of detector device at each pH needs to be registered to obtain pKa.
• Experimental equipment has lower cost because of exclusion of monochromator device and diode array.
• Method is suitable for determination pKa values for substances with low spectral change.

An express method for determination of acidity constants of organic acids, based on the analysis of the integral transmittance vs. pH dependence is developed. The integral value is registered as a photocurrent of photometric device simultaneously with potentiometric titration. The proposed method allows to obtain pKa using only simple and low-cost instrumentation. The optical part of the experimental setup has been optimized through the exclusion of the monochromator device. Thus it only takes 10–15 min to obtain one pKa value with the absolute error of less than 0.15 pH units. Application limitations and reliability of the method have been tested for a series of organic acids of various nature.

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