As all alternative to the classical approach of combining strong cation exchange SCX-LC and RP-LC for the separation of complex proteomic samples, this essay describes the online comprehensive RP-LC x RP-LC separation of BSA and human blood serum. High orthogonality and peak capacity are achieved through the application of a significantly different pH in the two dimensions. The coupling of fused-core columns in series ensures high efficiency in the first dimension, while a previously designed interface with parallel second dimension columns further enhances the separation capability of the comprehensive system.