D) was acquired from Cambridge Isotopes (Andover, MA). Sodium phosphate
dihydrate, sodium phosphate monohydrate, sodium chloride, and formic
acid (FA) were purchased from Sigma-Aldrich (St. Louis, MO). Ethylene
glycol ReagentPlus (>99%) was purchased from Alfa Aesar (Ward Hill,
MA). The analytical sample used for these experiments was a tryptic
digest of fully reduced and iodoacetamide alkylated BSA (Thermo Scientific
Pierce BSA Protein Digest Standard, LC–MS grade, catalog no.
88341).