TPEN (Tetrakis-(2-pyridylmethyl)ethylenediamine) is an excellent heavy metal chelator while it does not affect Ca2 , Mg2 , Na , or K concentrations. Thus, TPEN is a useful tool to identify effects of heavy metals (Zn2 , Fe2 /Fe3 , Cu2 , and Mn2 , etc.) on fluorescent indicators of Ca2 , Mg2 , Na , or K .
