The present invention makes use of unique tags of a specific biopolymer that can be exploited for determining the concentration the biopolymer in crude solutions. In preferred embodiments the biopolymer is either a protein or a polynucleotide. Particularly, the invention provides a method for the determination and quantitation of biomolecules in crude mixtures by way of a separatioln technique in combination with mass spectroscopy. In one general embodiment, a target biomolecule is selected for analysis and an analog thereof is generated. Peak area integration of the peptide pairs provides a direct measure for the amount of target protein in the crude solution.