Field Determination of Phosphate in Environmental Water by Using a Hand-Powered Paper Centrifuge for Preconcentration and Digital Image Colorimetric Sensing

Table 2

Determination of water samples with the proposed PMB-SPE method and a standard PMB method.

Sample	PMB-SPE method, μM^a	Standard PMB method, μM	t value^b
Lake 1	ND	ND	—
Lake 2	2.50 ± 0.25	2.43	0.48
Lake 3	ND	0.06	-
Huajiang river	1.27 ± 0.12	1.15	1.73
Groundwater	0.30 ± 0.04	0.31	0.43

^aMean ± standard deviation, n = 3. ^bt critical value (, f = 2) = 2.92.