Fig. 6

Long-term stability of standards. A Longitudinal study design of stability evaluation of the Quartet standards. B Number of proteins identified monthly at 15 different time points. Left panel: peptide standards; Right panel: protein standards. C Pearson’s correlation coefficients matrix representing the correlation coefficients between the different mass spectrometry runs generated across 15 months using the Quartet standards (left panel: peptide standards; right panel: protein standards). D Reproducibility of proteins within different intensity groups and the global group during 15-month monitoring (left panel: peptide standards; right panel: protein standards). E Quantitative expression patterns of some proteins over 15 months. Left panel: proteins with high stability over 15 months; right panel: proteins with a degradation trend, especially after 12 months