In situ Raman spectroscopy methods and systems for characterizing or quantifying a protein purification intermediate and/or final concentrated pool during production or manufacture are provided. In one embodiment, in situ Raman spectroscopy is used to characterize or quantify protein purification intermediates critical quality attributes during downstream processing (i.e., after harvest of the protein purification intermediate). For example, the disclosed in situ Raman spectroscopy methods and systems can be used to characterize and quantify protein purification intermediates as the protein purification intermediates are purified, condensed, or otherwise formulated into the final drug product to be sold or administered.