Fluorescence Techniques in the Microdetermination of Metals in Biological Materials. Utility of 2, 4-Bis-[N,N´-di-(carboxymethyl)aminomethyl] Fluorescein in the Fluorometric Estimation of Al+3, Alkaline Earths, Co+2, Cu+2, Ni+2, and Zn+2 in Micromolar Concentrations.