A novel approach for the determination of the total concentration of acids in aqueous solutions by simultaneous diffusion limited current for reduction of acids and pH measurements

A novel method is presented for the detection of acid content in aqueous solutions. The method is based on simultaneous measurements, in the test solution, of the overall steady-state limiting current arising from the reduction of the acids, and pH, along with the use of a theoretical expression. The current is recorded with platinum microelectrodes, while pH is measured with glass electrodes. To relate current and pH data, an "amperometric calibration" of the glass electrodes is performed. Calibration equations are obtained from a series of combined current/pH measurements in solutions containing a range of concentrations of the strong acid HClO4. This procedure overcomes the problems associated with the unknown activity coefficient of H+ and liquid junction potential contributions involved in the pH measurements. The new methodology is tested in several aqueous solutions containing mono- and polyprotic acids either alone or in mixture; buffered solutions are also considered. It is shown that, under the latter conditions, special cases exist, in which the total acid concentration is achieved by overall steady-state limiting current measurements alone. The accuracy of the proposed method is tested against classical titration procedures. The discrepancies between the two methods do not exceed similar to5%. (C) 2001 Elsevier Science B.V. All rights reserved.