Abstract: A method and an apparatus for separating the constituents of a complex mixture of proteins, for example an organic fluid, such as blood plasma, to submit to proteomic analysis. The method comprises, in particular, a step of distributing the complex mixture of proteins on a determined number n of separation elements different from each other (101). Each separation element separates a determined group of proteins from the other proteins present in the complex mixture (102) according to determined criteria. The proteins thus isolated from each separation element are diluted and neutralised (103) for being then sent to an analytic instrument, for example a column for high resolution liquid chromatography, or HPLC (104b), and then a spectrometer of MS type, or of MS/MS type. Each separation element has particular chemical-physical features that capture by adsorption only the proteins belonging to a determined group, i.e. having similar features.