Magnetic nanoparticles coated with non-ionic surfactants as restricted access material for solid phase extraction

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Restricted access materials (RAMs) are sorbents with enhanced selectivity due to their inherent structure since their extractive groups are protected by external functional groups that exclude macromolecules by a size exclusion and/or an electrostatic repulsion mechanism. Thus, only the small target analytes are able to reach the extracting phase avoiding the clogging of the sorbent by the sample matrix.

In a recent article accepted for publication in Journal of Chromatography A (1), researchers from Wuhan at China have proposed a new RAM based on the combination of magnetic nanoparticles and non-ionic surfactants. Magnetite nanoparticles (Fe304), which are synthesized by an oxidative-coprecipitation method, are the core of these RAMs providing them with a paramagnetic behavior which is essential for their easy isolation after the extraction process. The magnetite particles, with sizes in the low nm range, are subsequently derivatized with dodecyltriethoxisilane anchoring C12 extractive groups to their surface. Finally, a non-ionic surfactant is coated to the surface by a self-assembly process, producing a size-exclusion network that protects the extractive groups from the sample matrix components. In addition to the selectivity enhancement, the non-ionic surfactant coating improves the dispersibility of the RAM in the sample reducing the aggregation tendency of the hydrophobic particles in aqueous media.

In this article two series of non-ionic surfactants, Tween and Span series, were evaluated. Tween surfactants (TW-20, TW-40, TW-60 and TW-85) provide a better performance than Span surfactants (SP-40 SP-60 SP-80) due to their higher hydrophilic-lipophilic balance (HLB) which facilitates their dispersion in an aqueous media. The selectivity enhancement of the proposed RAM is evaluated in complex samples like urine where steroid hormones are determined with good sensitivity and precision levels.

These RAMs based on the combination of magnetic nanoparticles and non-ionic surfactants are quite promising according to their easy synthesis and their good extraction performance. In the article, the readers will find some additional and interesting information concerning the synthetic process as well as the different performance of the surfactants evaluated. Moreover, the optimization process clearly identified the effect of different experimental conditions.

References:
(1) Restricted-access nanoparticles for magnetic solid-phase extraction of steroid hormones from environmental and biological samples. Link

Related posts:
(I) Hydrophilic-carbonaceous magnetic nanoparticles coated with chitosan. Link

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