Colorimetric determination of trace orthophosphate in water by using C(18)-functionalized silica coated magnetite

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.