Mixed sorbent in miniaturized stir bar sorptive dispersive microextraction for the determination of gut microbiome metabolites in plasma samples

An analytical method for the simultaneous determination of three gut microbiome metabolites related to the gut-brain axis (trimethylamine N-oxide (TMAO), phenylacetylglutamine (PAG), and 4-ethylphenyl sulfate (EPS)) in human plasma is presented. The proposed method is based on miniaturized stir bar sorptive dispersive microextraction (mSBSDME) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this work, a magnetic composite made of CoFe₂O₄ magnetic nanoparticles embedded into a mixture of commercial sorbents (hydrophilic-lipophilic balance and mixed-mode cation exchange) was employed as magnetic sorbent material, taking advantage of its affinity to the target analytes. Under the optimized conditions, the method was validated and showed good analytical features in terms of linearity (at least up to 1000 ng mL^-1), limits of detection (22, 2, and 9 ng mL^-1 for TMAO, PAG, and EPS, respectively), repeatability (RSD ≤ 10%), and accuracy (91-101%). Moreover, relative recoveries between 84 and 104% were obtained, showing matrix effects were negligible using deuterated standards as surrogates. This new approach was successfully applied to clinical samples, allowing the rapid determination of the target metabolites in a single run for the first time.