The peak was present in coastal and estuarine samples but was removed upon UV digestion, with no peak in the range of 0 to −0.6 V in UV–SW with 20 nM Cu until HA was added. HA addition to the UV–SW without added copper caused a peak by the Cu-complex with the background Cu concentration in the UV–SW (1.7 nM) which increased significantly with nanomolar Cu additions.y