Figure 1. Sensitivity of probe response to measured equilibrium.

Simulated probe responses for titration of metal ions into: (a) a solution containing a metal probe P (10 µM) with K_D(P) = 5 × 10ⁿ (n = 0, ±1, ±2,…) µM; (b) a solution containing an equimolar concentration of metal probe P and competing ligand L (each 10 µM; the case 3 in Table 1) where $m=\log K_{\mathrm{D}(\mathrm{P})}/K_{\mathrm{D}(\mathrm{L})}$; (c) the same as (b) but [L] = 55 µM (the case 2 in Table 1); (d) the same as (b) but [L] = 505 µM (the case 1 in Table 1). In each case, the dashed lines mark the 20%, 50% and 80% probe responses. The probe response (PR%) at [metal]/[probe] = 1 for each titration curve with specific value n in (a) or m in (b–d) is also indicated.