SIMULTANEOUS DETERMINATION OF FE(II) AND FE(III) IN SOLUTION IN PRESENCE OF SODIUM-CHLORIDE AND CALCIUM-CHLORIDE

Two-component complexometric potentiometric titration has been applied in the simultaneous determination of Fe(II) and Fe(III) in the NaCl and CaCl2 matrices. The end-points have been read directly from the titration curve. Because of the matrix effect the crude analytical results were biased. They have been effectively corrected using a set of two calibration equations which approximated the relationship between the end-points found and the true concentrations of analytes in the solution. The regression coefficients in the equations have been determined on the basis of the titration data obtained for standard solutions, compositions of which corresponded to a factorial plan. The influence of the calibration model and composition of the standard solutions on the quality of analytical results has been examined. The effect of the matrix concentration on the determination error has been tested.