Dispersive micro-solid phase extraction of ortho-phosphate ions onto magnetite nanoparticles and determination as its molybdenum blue complex

A direct microextraction method, employing dispersive micro-solid phase extraction (μ-SPE) of ortho-phosphate (o-PO43−) anions onto ferromagnetic nanoparticles (MNPs) is described in this work for the first time. The method exploits the complexation of phosphate ions on the surface of positively charged magnetite nanoparticles through the formation of an inner sphere complex, which are separated from the bulk aqueous phase with the application of an adscititious magnetic field. Phosphates are eluted with sodium bicarbonate and determined spectrophotometrically as their phosphomolybdenum blue complex. The method is generally free from common interferences, likely to affect the measurement of phosphate, since it alleviates their presence already from the extraction step, thus they are absent during detection. The detection limits are as low as 0.01 μM with very satisfactory precision ranging from 3.68% (intra-day) to 8.5% (inter-day) and accuracy between 91.5% and 104.8%.