Some metals, such as, Ag + , Hg 2+ and Ni 2+ displayed an increasing trend in normalised fluorescence with pH, while other metal ions, such as Pb 2+ , Fe 3+ , Zn 2+ Mn 2+ and Cd 2+ displayed higher normalised fluorescence values at lower pH environments, a trough in intensity at neutral pH, then an increase at higher pH values (Figure 2 d).
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