Colorimetric determination of trace orthophosphate in water by using C18-functionalized silica coated magnetite

Abstract

Abstract In this study, we customized magnetic sorbents by functionalizing silica coated magnetite with octadecyl(C 18 )silane (Fe 3 O 4 @SiO 2 @C 18 ). This sorbent was intended for the determination of trace orthophosphate ( o -PO 4 3− ) in unpolluted freshwater samples. The o -PO 4 3− was transformed to phosphomolybdenum blue (PMB), a known polyoxometalate ion. Then the PMB were coupled with cetyl trimethyl ammonium bromide (CTAB), cationic surfactant, in order to hydrophobically bound with the Fe 3 O 4 @SiO 2 @C 18 particles through dispersive magnetic solid-phase extraction (d-MSPE) as part of sample preconcentration. The PMB–CTAB–magnetic particles are simply separated from the aqueous solution by the external magnet. The acidified ethanol 0.5 mL was used as PMB-CTAB eluent to produce an intense blue solution, which the absorbance was measured using a UV–Vis spectrophotometer at 800 nm. The proposed method (employing 2 mg of Fe 3 O 4 @SiO 2 @C 18 ) yielded an enhancement factor of 32 with a linear range of 1.0–30.0 µg P L −1 . Precision at 6.0 µg P L −1 and 25.0 µg P L −1 were 3.70 and 2.49% (RSD, n = 6) respectively. The lower detection limit of 0.3 µg P L −1 and quantification limit of 1.0 µg P L −1 allowed trace levels analysis of o -PO 4 3− in samples. The reliability and accuracy of the proposed method were confirmed by using a certified reference material. Our method offers highly sensitive detection of o -PO 4 3− with simple procedures that can be operated at room temperature and short analysis time.