proteomic profiling by mass spectrometer label-free quantification LFQ A proteomic profiling method that uses mass spectrometry to quantify the relative amount of each protein across multiple biological samples without the need for any prior sample labelling. The assay is run separately on each sample and involves digestion of the proteome into peptides, liquid chromatography with mass spectrometry, and then quantification via spectral counting (i.e., the number of matching spectra from MS/MS) or integration of the intensities of each peptide's peaks. label-free protein quantification paola