Abstract: In the present paper, the characteristic of chemical process and methods of the decrement and the elimination of the plank in Isotope Dilution Mass Spectrometry (IDMS) are given. Usual methods of the purfication of agents such as distillation, Subboiidistillation, isothermal equilibrium, low temperature evaporation with touble nylon bottle, ion—exchange, sulfhydryl cotton fiber absorption and the method for the elimination of the plank with rouble samples are described in dital.