839498.fig.008
Figure 8: UV-visible spectra of (a)  M MG in aqueous solution of KCl without pH adjustment; (b)  M MG in aqueous solution of KCl at pH 1.70, and (c)  M MG chemically oxidized by 1.0 M H2SO4 +  M PbO2 + HClO4 in aqueous solution of KCl at pH 1.70.