Liquid chromatography (LC) coupled with mass spectrometry (MS) has been widely used for protein expression quantification. Protein quantification by tandem-MS (MS/MS) uses integrated peak intensity from the parent-ion mass (MS1) or features from fragment-ions (MS2). Label-free quantification (LFQ) may be based on precursor ion intensity (peak areas or peak heights) or on spectral counting. Here, the