Submicrometric Magnetic Nanoporous Carbons Derived from Metal-Organic Frameworks Enabling Automated Electromagnet-Assisted Online Solid-Phase Extraction

We present the first application of submicrometric magnetic nanoporous carbons (mu MNPCs) as sorbents for automated solid-phase extraction (SPE). Small zeolitic imidazolate framework-67 crystals are obtained at room temperature and directly carbonized under an inert atmosphere to obtain submicrometric nanoporous carbons containing magnetic cobalt nanopartides. The mu MNPCs have a high contact area, high stability, and their preparation is simple and cost-effective. The prepared mu MNPCs are exploited as sorbents in a microcolumn format in a sequential injection analysis (SIA) system with online spectrophotometric detection, which includes a specially designed three-dimensional (3D)-printed holder containing an automatically actuated electromagnet. The combined action of permanent magnets and an automatically actuated electromagnet enabled the movement of the solid bed of particles inside the microcolumn, preventing their aggregation, increasing the versatility of the system, and increasing the preconcentration efficiency. The method was optimized using a full factorial design and Doehlert Matrix. The developed system was applied to the determination of anionic surfactants, exploiting the retention of the ion-pairs formed with Methylene Blue on the mu MNPC. Using sodium dodecyl sulfate as a model analyte, quantification was linear from 50 to 1000 mu g L-1, and the detection limit was equal to 17.5 mu g L-1, the coefficient of variation (n = 8; 100 mu g L-1) was 2.7%, and the analysis throughput was 13 The developed approach was applied to the determination of anionic surfactants in water samples (natural water, groundwater, and wastewater), yielding recoveries of 93% to 110% (95% confidence level).