The analytical power of the differential impedance analysis (DIA) as a new approach for model identification is investigated. The minimum of the ratio q of the two time-constants T-1 and T-2 (q = T-1/T-2) describing a two step reaction with la Ider Structure, at which the second time-constant T-2 is recognized, is accepted as a measure for the selectivity evaluation. The investigation is performed on synthetic models with variation of q in the interval from 30 to 0.001. The influence of data quality is studied by applying data truncation from seven to two digits, as well as by introduction of a wild point. Experimental data measured on two actual dummy cells with q equal to 30 and 0.03, respectively, are also analyzed. The results are compared with those obtained by applying the algorithm of the wide-spread complex non-linear least-squares method, performed on zview software product. The comparative study demonstrates a higher selectivity of the DIA, combined with an additional noise immunity and increased robustness of the analysis.