Figure 1. Dependence on H₂SO₄ concentration.

(A) Color development curves determined at 710 nm for different concentrations of sulfuric acid: 12.5 mM (a), 41.7 mM (b), 55.6 mM (c), 139 mM (d), 167 mM (e), 194 mM (f), 222 mM (g) and 625 mM (h). The arrow indicates the addition of 15 nmol of Pi to the cuvette. (B) Dependence of absorbance (•, ▴, ▪) or color development rate (○) on acid concentration. Absorbance data were taken from the color development curves at t = 15 min (•) or from the visible spectra (Fig. S1) at 710 nm (▴) or 890 nm (▪). The dashed lines indicate the optimal concentration range (see also Table 1).