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

In this study, we customized magnetic sorbents by functionalizing silica coated magnetite with octadecyl(C-18)silane (Fe3O4@SiO2@C-18). This sorbent was intended for the determination of trace orthophosphate (o-PO43-) in unpolluted freshwater samples. The o-PO43- 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 Fe3O4@SiO2@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 Fe3O4@SiO2@C-18) yielded an enhancement factor of 32 with a linear range of 1.0-30.0 mu g P L-1. Precision at 6.0 mu g P L-1 and 25.0 mu g P L-1 were 3.70 and 2.49% (RSD, n = 6) respectively. The lower detection limit of 0.3 mu g P L-1 and quantification limit of 1.0 mu g P L-1 allowed trace levels analysis of o-PO43- 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-PO43- with simple procedures that can be operated at room temperature and short analysis time.

Automated summary

In this study, customized magnetic sorbents were successfully used for the determination of trace orthophosphate in unpolluted freshwater samples. The method involving phosphomolybdenum blue (PMB), cetyl trimethyl ammonium bromide (CTAB), and dispersive magnetic solid-phase extraction (d-MSPE) showed high detection sensitivity and simple operation procedures.