Elevated Plasma Albumin and Apolipoprotein A-I Oxidation under Suboptimal Specimen

S-cysteinylated albumin and methionine-oxidized apoli-poprotein A-I (apoA-I) have been posed as candidate markers of diseases associated with oxidative stress. Here, a dilute-and-shoot form of LC–electrospray ionization–MS requiring half a microliter of blood plasma was employed to simultaneously quantify the relative abundance of these oxidized proteoforms in samples stored at 80 °C, 20 °C, and room temperature and ex-posed to multiple freeze–thaw cycles and other adverse conditions in order to assess the possibility that protein oxidation may occur as a result of poor sample storage or handling. Samples from a healthy donor and a participant with poorly controlled type 2 diabetes started at the same low level of protein oxidation and behaved similarly; sig-nificant increases in albumin oxidation via S-cysteinyla