This expresses the number of peaks which can be resolved in a given part of the chromatogram between the peaks of two consecutive n-alkanes with z and (z + 1) carbon atoms in their molecules: \[\text{SN} = \frac{t_{\text{R}\left(z\,+\,1\right)}- t_{\text{R}z}}{w_{\text{h}z}\,+\,w_{\text{h}\left(z+1\right)}} - 1\] In the German literature the symbol TZ (trennzahl) is commonly used to express the separation number. As the separation number depends on the n-alkanes used for the calculation, they always must be specified with any given SN value.