This invention relates to methods and kits for positive selection of species of interest based on peptide/protein sequence from a biological sample. The species of interest may be proteins and/or peptides of interest which may be placed through a mass spectrometer to obtain a blood peptide/protein signature. The blood peptide/protein signature may be used in proteomic analysis. The techniques include but are not limited to the use of collectors comprising nucleic acid molecules to extract a composition that has a lower concentration of a high abundance species of interest from a sample. This limits the level of influence that any collectors species may have on the results of a mass spectra.