CuL candidates identified by LC-Orbitrap analyses were extracted from the LC-FT-ICR MS data to obtain ultrahigh resolution m/z to allow for the unambiguous assignment of molecular formulae. Metal-free ligands were found by searching for the presence of a molecular ion at a m/z occurring at 61.92177 Da or 60.91395 Da lower than the m/z of CuL complex, which correspond to the Cu(I) or Cu(II) oxidation states. All metal-free ligands identified were present at m/z 60.91395 lower than the CuL, indicating a +2 oxidation state of the Cu. Elemental compositions were assigned using the Predator Molecular Formula Calculator (v.1.3.3), with elemental constraints of C∞H∞O0-15N0-10Cu1 ± 2.5 ppm for CuLs and C∞H∞O0-15N0-10 ± 2.5 ppm for metal-free ligand assignments. No 34 S isotope peak was observed for any Cu or metal-free ligands, therefore sulfur was excluded from elemental constraints.