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 MaxLFQ algorithm is applied, which relies on chromatographic ion intensities.