Atmospheric monitoring of methane shows that CH4 concentration growth since 2007 is accompanied by C13/C12 isotopic delta ratio shift to more negative values due to 13CH4 content depletion. In the work, the atmospheric total column amount and vertical profiles of 13CH4 and 12CH4 are retrieved from the ground-based measurements of solar spectra in Kourovka observatory. The CH4 isotopologues ratio is calculated. The error of the isotopologues content retrieval is estimated for different spectral regions. On basis of the obtained results, optimal spectral windows were found.