Standards of o-Tyr, p-Tyr, Phe, 3NO2-Tyr, 3Cl-Tyr, 8OHdG and 2dG (>96% w/w purity) were from Sigma-Aldrich (St. Louis, MO, USA). Internal standards (ISs) p-Tyr-D2, 2dG-13C15N2, and 8OHdG-13C15N2 were acquired from Cambridge Isotope Laboratories and Phe-D5 from CDN Isotopes (Pointe-Claire, Canada).
Individual stock solutions of o-Tyr (2 mM), 3NO2-Tyr (2 mM), 3Cl-Tyr (2 mM), 8OHdG (2 mM), 2dG (2 mM), 2dG-13C15N2 (5 mM), 8OHdG-13C15N2 (5 mM), Phe-D5 (10 mM) and Phe (75 mM) were prepared and dissolved as previously described [21 (link)]. Once prepared, solutions were stored at −20 °C. Multi-component working solutions were prepared and kept at −20 °C. Standard solutions were prepared by serial dilution of the working solutions. The preparation of the standards and reagents that we used were described in detail by Cascant-Vilaplana and colleagues [21 (link)].
Individual stock solutions of o-Tyr (2 mM), 3NO2-Tyr (2 mM), 3Cl-Tyr (2 mM), 8OHdG (2 mM), 2dG (2 mM), 2dG-13C15N2 (5 mM), 8OHdG-13C15N2 (5 mM), Phe-D5 (10 mM) and Phe (75 mM) were prepared and dissolved as previously described [21 (link)]. Once prepared, solutions were stored at −20 °C. Multi-component working solutions were prepared and kept at −20 °C. Standard solutions were prepared by serial dilution of the working solutions. The preparation of the standards and reagents that we used were described in detail by Cascant-Vilaplana and colleagues [21 (link)].