Table 2. Calibration curves.

Sodium citrate	Pi concentration range	Intercept	Slope	R	Estimated ε
	(nmol)		(nmol -1)		(M-1cm-1)
–	0–100	–0.008(1)	0.02048(5)	0,99953	2.05·105
+	0–2	0.001(1)	0.0202(9)	0.99947	2.0·105
+	0–40	0.0020(5)	0.01905(6)	0.99983	1.90·105
+	40–100	0.155(8)	0.0153(1)	0.99905	1.5·105

Fitting parameters for experimental data reported in Fig. 6. The uncertainty on the last digit is indicated between parenthesis.