We report a dispersive liquid–liquid microextraction (LLME) method using surface modified Mg(OH)2 nanoparticles (NPs) with oleic acid (OA) as hydrophobic affinity probes for the extraction and preconcentration of hydrophobic biomolecules prior to MALDI MS analysis. OA-capped Mg(OH)2 NPs were characterized by FT-IR, SEM and TEM. The functionalized Mg(OH)2 NPs are well dispersed in toluene with an average diameter of <35 nm. Under the optimum conditions, the method showed good linearity in the ranges of 10–400 nM and 0. 1–2.0 μM for valinomycin and gramicidin D, respectively. The limits of detection were in the region of 2.0 nM and 24 nM for valinomycin and gramicidin D, respectively. Moreover, the OA-capped Mg(OH)2 NPs-assisted LLME method was successfully used for the rapid extraction/preconcentration of hydrophobic proteins in bacteria (Escherichia coli and Bacillus subtilis) prior to their identification by MALDI MS.
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