A method for the analysis of isotope ratios, wherein at least one sample gas and/or at least one reference gas are supplied to at least one analytical device via at least one open split, the addition of a carrier gas also being possible. According to the invention, the concentration of the sample gas and/or reference gas passing into the analytical device is controlled by the supply of the respective carrier gas or by direct supply of the sample gas into the analytical device. In the device according to the invention for supplying gases to at least one analytical device, two or more capillaries are provided for sample gases, the capillaries in each case having their own drive for the movement between mixing zone and waiting zone.