Table 5. Measurement of zinc concentrations in various water samples.

Sample	Added (ng mL−1)	Founda (ng mL−1)	Recovery (%)	FAASa (ng mL−1)	t-Testb	F-Valuec
Tap waterd	—	2.3 ± 0.1g	—	2.3 ± 0.2g
	75.0	78.0 ± 0.1	100.91	76.5 ± 0.3	1.55
	150.0	151.5 ± 0.2	99.47	12.1 ± 0.4		3.23
River watere	—	10.5 ± 0.3	—	10.4 ± 0.8
	125.0	134.0 ± 0.2	98.89	137.5 ± 0.7		3.59
	250.0	265.5 ± 0.4	101.92	257.5 ± 0.6	1.67
Sea waterf	—	15.5 ± 0.3	—	15.5 ± 0.5
	200.0	213.0 ± 0.2	98.84	219.0 ± 0.9	1.42
	400.0	420.5 ± 0.3	101.20	408.0 ± 1.2		3.05
Well waterd	—	7.6 ± 0.1	—	7.5 ± 0.2g
	250.0	261.0 ± 0.2	101.32	252.0 ± 0.2		3.73
	500.0	501.5 ± 0.2	98.80	515.0 ± 0.2	1.57
Waste waterc	—	72.5 ± 0.3	—	72.7 ± 2.3
	225.0	300.5 ± 0.6	101.01	295.0 ± 0.9	1.28
	450.0	520.0 ± 0.2	99.52	527.0 ± 1.2		2.87

^aAverages ± standard deviations of six determinations.

^bThe critical t-value (α = 0.05, df = 5) = 2.57.

^cThe critical F-value (α = 0.05, df = 5) = 5.05.

^dCollected from Zagazig, Egypt.

^eCollected from Benha, Egypt.

^fCollected from Alexandria, Egypt.

^gAfter preconcentration.