be decreased, resulting in a higher percentage of unambiguous formula assignments. The Cucontaining ions ranged in m/z from 237 to 689 and all contained 1-5 N atoms. In addition to N, 12, 17, and 34 of the molecular ions also contained O (without S), S (without O), or both O and S, respectively. To date, only one study has provided deeper insight to the structural characteristics of a CuL isolated from seawater. Using a combination of FT-ICR MS and inductively coupled plasma mass spectrometry (ICP MS) coupled to liquid chromatography (LC), an abundant CuL with the molecular formula [C20H21N4O8S2Cu] + was isolated from seawater collected in the Eastern Tropical Pacific Ocean. Based on high resolution fragmentation data, the authors concluded that the ligand had heavily conjugated, cyclic, azolelike functional groups, that the sulfur was present as thiols, and that the Cu was complexed by N. The O:C (0.4) and N:C (0.2) ratios of this CuL are consistent with a peptide-like compound, with a high degree of unsaturation.