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Table 1
The relative standard deviation in the determination of ferric ions (%)
Ferric ions (mg/L)	Within the day		RSD (%)	Between days		RSD (%)
	A480			A480
	Mean	SD		Mean	SD
0	0.0458	0.0027	5.93	0.0462	0.0025	5.32
0.31	0.0540	0.0008	1.48	0.0554	1.90 × 10⁻³	3.43
0.62	0.0665	0.0031	4.68	0.0682	0.0038	5.58
1.25	0.0878	0.0013	1.47	0.0894	2.00 × 10⁻³	2.25
2.5	0.1301	0.0029	2.23	0.1329	0.004	2.97
5	0.2187	0.0049	2.25	0.2253	0.0093	4.13
10	0.4111	0.0084	2.03	0.4219	0.0127	3.02
20	0.8206	0.0297	3.61	0.846	0.0343	4.05
40	1.6834	0.027	1.60	1.6896	0.0202	1.20
80	3.442	0.0633	1.84	3.4985	0.0851	2.43
100	4.2956	0.0671	1.56	4.3911	0.1499	3.41
200	5.9739	0.036	0.60	5.9739	0.036	0.60

The RSD at different concentrations of ferric ions was the relative percentage of the standard deviation with mean value calculated from three determinations of ferric ions in 1 day or 3 days, respectively.

Wu et al. Nanoscale Research Letters 2012 7:665 doi:10.1186/1556-276X-7-665

Table 1