Copper ligands (CuLs) isolated from spent P. tricornutum medium include an unresolved complex mixture of CuLs that appear as a gradual rise and fall in the baseline of the LC-ICP MS 63 Cu chromatogram topped with a number of defined peaks (Fig. ). To identify molecular ions corresponding to CuL complexes, samples were analyzed by LC-Orbitrap using the same chromatographic conditions. CuLs were identified based on the mass difference and RA of 63 Cu and 65 Cu peaks and alignment with the LC-ICP MS chromatogram. Eleven putative CuLs (A-K) were identified, with m/z ratios between 521 and 720 that elute between 19 and 38 minutes (Fig. ). In order to confirm the presence of Cu and assign a molecular formula to these putative CuLs, higher resolution m/z were required.