Fig. 3.

a Continuous variation plot at three representative wave-lengths for the Yb³⁺ and PV system in 10 mM HEPES buffer at pH 7.0. The total concentration of Yb³⁺ + PV is equal to 100 µM. Samples were prepared by adding the acidic stock solutions to the buffer. b Absorbance difference at 623 and 443 nm as a function of the [Yb³⁺]/[PV] molar ratio. The PV concentration was kept constant at 50 µM, and Yb³⁺ was varied from 0 to 100 µM