The database search results for both samples were investigated in-depth to gain more insight into the identifications and their quality. On the peptide level, both samples had very similar identifications. Specifically, 501 peptides were identified in both samples, and only 68 peptides were identified in only one of the samples (Figure 2 A). On the protein level, both samples managed to identify 35 common proteins and 1 unique protein in each sample (Figure 2 B). Cytochrome C was identified as a unique protein in sample A11-12042 and Ubiquitin-conjugating enzyme E2 C in sample A11-12043. Both proteins had a concentration of 0,005 pmol in the UPS2 standard. In general, it can be observed that the concentration of the proteins in the UPS2 samples influences the probability of identifying a protein. In both samples, the proteins with a concentration of 0,5, 5 and 50 pmol were all detected. As the concentrations of the proteins was reduced, the percentage of detected proteins also decreased up to a point that all proteins with a concentration of 0,0005 pmol remained undetected (Figure 2 C). The same phenomenon was observed when looking into the coverage of the proteins. While both samples had somewhat equal coverages, it is visible that as the concentration of the proteins decreases, so does the coverage (Figure 2 D). Proteins with a concentration of 50 pmol were almost always identified with a coverage above 90%, except for the protein Complement C5 being an outlier for both samples. Proteins with a concentration of 0,005 pmol almost always had a coverage well below 10% for both samples apart from GTPase HRas in sample A11-12043, having a coverage of 20,11%.