4.

Peak areas obtained from the XICs of different ARP-derivatized peptides normalized to the corresponding region in the underivatized negative control (Neg. Ctrl.). Heatmap of the normalized peak areas of all 86 carbonylated peptides in all 68 donor and quality control serum samples (A) and box plots grouped by sample type (B). Peak area distributions are shown for selected precursor ion signals corresponding to the ARP peptides LQQC­[+369.147]­PFEDHVK (C), LK­[+395.137]­C­[+57.021]­ASLQK (D), K­[+385.142]­QTALVELVK (E), and ATK­[+369.147]­EQLK (F). Red horizontal lines in the heatmap correspond to precursor ions with integration interference that prevented detection; sample and precursor ion IDs are provided in Table S7. Log₂-transformed ratios are used as a color fill gradient. The inflection point of the gradient corresponds to log₂(3). In the box plots, dark blue and dark red lines represent the y-intercepts at log₂(10) and log₂(3), respectively.