Table 2.

Accuracy assessment for calibration curves prepared in triplicate and back calculating the pH based on the sigmoidal curve fit parameters (Table 1) and Equation 2

Curve #1				Curve #2				Curve #3
Exp. pH	Abs. Ratio (590 nm/520 nm)	Calc. pH	Accuracy (% bias)	Exp. pH	Abs. Ratio (590 nm/520 nm)	Calc. pH	Accuracy (% bias)	Exp. pH	Abs. Ratio (590 nm/520 nm)	Calc. pH	Accuracy (% bias)
8.84	2.183	8.84	100.0%	8.90	2.162	8.63	97.0%	8.86	2.179	8.79	99.2%
8.38	2.148	8.52	101.6%	8.36	2.144	8.49	101.5%	8.39	2.090	8.17	97.4%
7.94	2.028	7.91	99.6%	7.89	2.027	7.91	100.2%	7.94	2.044	7.97	100.4%
7.62	1.955	7.68	100.8%	7.52	1.927	7.60	101.1%	7.56	1.904	7.54	99.8%
7.36	1.841	7.40	100.5%	7.35	1.833	7.38	100.4%	7.33	1.812	7.33	100.1%
7.23	1.757	7.22	99.9%	7.14	1.750	7.21	101.0%	7.30	1.746	7.20	98.7%
7.16	1.717	7.15	99.9%	7.09	1.675	7.08	99.8%	7.09	1.686	7.10	100.1%
6.97	1.640	7.02	100.7%	6.98	1.641	7.02	100.5%	7.00	1.629	7.00	100.0%
6.90	1.569	6.90	100.0%	6.83	1.542	6.86	100.4%	6.85	1.558	6.88	100.5%
6.79	1.487	6.77	99.7%	6.72	1.466	6.74	100.3%	6.80	1.446	6.71	98.7%
6.61	1.354	6.58	99.5%	6.48	1.308	6.51	100.4%	6.64	1.372	6.60	99.4%
6.50	1.287	6.48	99.7%	6.37	1.242	6.41	100.7%	6.50	1.286	6.48	99.6%
6.30	1.198	6.35	100.8%	6.30	1.197	6.35	100.8%	6.38	1.195	6.35	99.5%
6.26	1.099	6.20	99.1%	6.24	1.081	6.18	99.0%	6.20	1.097	6.20	100.0%
6.13	1.008	6.06	98.9%	6.02	0.992	6.04	100.3%	6.01	0.976	6.01	100.1%
5.82	0.876	5.85	100.5%	5.84	0.879	5.85	100.2%	5.89	0.893	5.88	99.8%
5.58	0.724	5.56	99.6%	5.56	0.736	5.58	100.4%	5.58	0.732	5.57	99.9%
5.08	0.559	5.13	101.1%	5.08	0.563	5.15	101.3%	5.19	0.568	5.16	99.5%
4.38	0.416	4.50	102.7%	4.34	0.419	4.52	104.1%	4.52	0.448	4.69	103.7%

Tabulated pH data spans a range of 4.38–8.90 because the precision (%Bias) over this pH range was between 97.0%–104.1%.