A novel approach for the determination of the total concentration of acidsin 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 so lutions. The method is based on simultaneous measurements, in the test solu tion, of the overall steady-state limiting current arising from the reducti on of the acids, and pH, along with the use of a theoretical expression. Th e current is recorded with platinum microelectrodes, while pH is measured w ith glass electrodes. To relate current and pH data, an "amperometric calib ration" of the glass electrodes is performed. Calibration equations are obt ained from a series of combined current/pH measurements in solutions contai ning a range of concentrations of the strong acid HClO4. This procedure ove rcomes the problems associated with the unknown activity coefficient of Hand liquid junction potential contributions involved in the pH measurements . The new methodology is tested in several aqueous solutions containing mon o- and polyprotic acids either alone or in mixture; buffered solutions are also considered. It is shown that, under the latter conditions, special cas es exist, in which the total acid concentration is achieved by overall stea dy-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 Scien ce B.V. All rights reserved.