Fig. 8. (a) Absorption spectra of PPS (10 μM, DMSO–PBS, pH = 7.4, 8 : 2, v/v) with arginine (100 μM) and successive additions of KH₂PO₄ (0–100 μM). (b) Absorbance of PPS–arginine (10 : 100 μM, DMSO–PBS, pH = 7.4, 8 : 2, v/v) at 410 nm vs. increasing concentration of H₂PO₄⁻.