Abstract: A general computer program, SCTPT, written in FORTRAN IV, is described which uses Marquardt-Fletcher modification of Gauss-Newton method to calculate the stability constants of the type M_iA_iH_kin two-phase solution from the pHtitrations. The minimization is perfomed with respect to the square of the titre and the analytical derivatives are employed. This program possesses high speed and good convergence.The close initial estimates are not required and can be varied in a range of 4-15 orders of magnitude. This program has been tested on the Cu-PMBP and Zn-PMBPextraction systems and found to be very convenient for use and gives satisfactory results.

Key words: Two-phase pH titrations, Mechanism of chelate extraction, General computer program