Magnetic nanoparticle assisted dispersive liquid–liquid microextraction for the determination of 4-n-nonylphenol in water

Abstract

A fast extraction technique involving dispersive liquid–liquid microextraction (DLLME) coupled with magnetic nanoparticle-based dispersive solid-phase microextraction (D-μ-SPE) was developed. For preliminary study, this method was applied for the extraction of 4-n-nonylphenol (4-NP) in water. In this method, n-octyl-triethoxysilane surface-modified magnetic iron oxide nanoparticles (C₈MNPs) were first synthesized. The DLLME was performed by injecting 1 mL of methanol (disperser) containing 10 μL of 1-octanol (extraction solvent) into 15 mL of water sample. To this solution, C₈MNPs were immediately added for the retrieval of the extraction solvent and of the extracted 4-NP by sonication. Subsequently, a magnet was held next to the vial to attract and isolate the C₈MNPs. Then, the water sample was decanted, the nanoparticles were freeze-dried, and the 4-NP was extracted from nanoparticles by sonication with methanol. The detection of 4-NP was performed using a HPLC coupled with a fluorescence detector. Under optimal extraction conditions, a low method of detection limit (13.9 ng L⁻¹), good linearity (R² = 0.9958), and repeatability (1.7–2.2%) were achieved during 4-NP extraction. This method was also successfully used to analyze the real water samples such as drinking water and secondary wastewater. Generally, this sample preparation method offered an alternative to the conventional DLLME, because, in this method, centrifugation is not required and the retrieval of the extraction solvent is based on the adsorption process by magnetic nanoparticles (MNPs). Also, this two-step method improved the versatility of DLLME because the selection of the extraction solvent was no longer limited to the high density solvents. Because MNPs can be surface-modified for the extraction of different organic solvents, this method could have great prospects in the future.