Solid-phase extraction of Cr(VI) with magnetic melamine–formaldehyde resins, followed by its colorimetric sensing using gold nanoparticles modified with p-amino hippuric acid

Abstract

A new method for magnetic solid-phase separation of trace-levels of Cr(VI) by using magnetic nanoparticles modified melamine–formaldehyde resin (Fe3O4@MFR) was described. Also, the selective and sensitive chemical optical probe was developed based on citrate-polyvinyl alcohol capped gold nanoparticle and modified with the reagent p-amino hippuric acid (PAH). Consequently, the optical probe was employed for the sensing of Cr(VI) ion in aqueous media. The sensing scheme is based on the complexation between PAH and reduced Cr(III). The linear calibration curve for Cr(VI) was calculated with preconcentration and was found in the range of 2.6–156 µg L−1 and the limits of detection for Cr(VI) were 10.4 µg L−1 and 2.0 µg L−1 with the naked eye and UV–vis spectroscopic detection, respectively. More importantly, both magnetic solid-phase extraction and colorimetric optical probe are selective for detection of the target analyte. The recoveries are between 96 and 99% when exercising 15 mg of the Fe3O4@MFR. The coupled approach was employed for the pre-concentration and quantification of Cr(VI) in two real water samples (tap water and mineral water) employing the standard addition protocol.