During 40Ar/39Ar dating, the age spectrum of the sample can be seriously distorted due to averaging of its Ar isotope composition over the fraction of gas released during the measurements. New methods of age spectrum approximation with suppression of distortions have been developed. The efficiency of these methods is experimentally demonstrated. A new high-resolution method for measuring age spectra from the fraction of gas released is proposed. This method is based on experimental data and permits refining the age spectrum or its fragments. The applicability and efficiency of this method are also shown experimentally. The proposed measurement method can be used not only to measure age spectra during 40Ar/39Ar dating but also to measure other isotope characteristics of rock and mineral samples during stepwise separation of analytes.