Figure 4.

(a) Circles, experimental calibration curves relative to 10 polymeric spots of TBB (curve 10), BB (curve 1), and their mixtures with molar ratio n_TBB/n_BB: 0.024, 0.061, 0.098, 0.147, 0.184, 0.233, 0.331 and 0.478 (curve 2–9). Continuous line, bi-sigmoidal fitting between pH 1 and 10. (b) Experimental profiles of the precisions, $s_{\mathrm{pH}}$, obtained from calibration curves 1 ($s_{{\mathrm{pH}}_{\mathit{BB}}})$, 5 ($s_{{\mathrm{pH}}_{\mathit{TBB}/\mathit{BB}}})$, 10 ($s_{{\mathrm{pH}}_{\mathit{TBB}}})$ and the overall ones, $s_{{\mathrm{pH}}_w}$.