The method for determination of the interface Proximity during depth profiling carried out using x-ray photoelectron spectroscopy and Auger electron spectroscopy in combination with ion etching is described. The optimization procedure is based on the additional registration of the true secondary electron peak (TSEP) taking into account that the true secondary electrons have greater escape depth and the peak energy position considerably depends on the work function alterations. The proposed method uses TSEP spectral characteristics that are capable of predicting the approach of the interface in advance compared to the traditional methods. Since the intensity of TSEP is much greater compared to that of Auger and photoelectron lines, then the time to register it is sufficiently less than the characteristic spectral acquisition time. On the other hand, the TSEP may be registered during ion etching as a result of ion-induced electron emission. The obtained results show that ion electron emission is very convenient for monitoring sputtering.