We are performing an eosin Y displacement assay wherein eosin Y is quenched by a copper(II) based macrocycle, then released by organic anions. The release causes recovery of fluorescence. If we have an anion that does not bind to the macrocycle, we find that it increases the quenching activity, rather than having no effect. Do you believe that this further reduction in fluorescence could be caused by the bulk solution ionic strength driving the eosin Y to bind to the quencher? This is a concentration dependent response, with more quenching seen at higher concentrations.