Table 2. Speciation Analysis of Fe²⁺/Fe³⁺ in Natural Water Samples.

	added (100 ppb)	found/ppba
sample	Fe2+/Fe3+ (ppb)	Fe2+	Fe3+	ICP-AES/ppba
tap water	blank	b
	20/80	18.42 ± 0.88	83.17 ± 0.27	105.23 ± 0.23
	50/50	47.38 ± 0.42	48.68 ± 0.32	97.18 ± 0.19
	80/20	76.91 ± 0.47	19.23 ± 1.04	95.95 ± 0.51
Yangtze River water	blank	1.42 ± 0.26		2.54 ± 0.34
	20/80	17.25 ± 1.12	81.55 ± 0.29	101.35 ± 0.45
	50/50	51.06 ± 0.50	54.64 ± 0.43	106.23 ± 0.36
	80/20	77.28 ± 0.21	21.27 ± 0.79	97.91 ± 0.57
Jianghan Plain groundwater	blank	2.04 ± 0.33	1.51 ± 0.24	3.69 ± 0.27
	20/80	16.39 ± 0.86	88.06 ± 0.62	98.37 ± 0.42
	50/50	47.71 ± 0.51	52.38 ± 0.56	102.39 ± 0.28
	80/20	82.13 ± 0.33	18.29 ± 0.84	105.37 ± 0.31

^aAverage of three measurements + standard deviation.

^bBelow the detection limit.