Innovations in Extractive Phases for In-Tube Solid-Phase Microextraction Coupled to Miniaturized Liquid Chromatography: A Critical Review

Over the past years, a great effort has been devoted to the development of new sorbents that can be used to pack or to coat extractive capillaries for in-tube solid-phase microextraction (IT-SPME). Many of those efforts have been focused on the preparation of capillaries for miniaturized liquid chromatography (LC) due to the reduced availability of capillary columns with appropriate dimensions for this kind of system. Moreover, many of the extractive capillaries that have been used for IT-SPME so far are segments of open columns from the gas chromatography (GC) field, but the phase nature and dimensions are very limited. In particular, polar compounds barely interact with stationary GC phases. Capillary GC columns may also be unsuitable when highly selective extractions are needed. In this work, we provide an overview of the extractive capillaries that have been specifically developed for capillary LC (capLC) and nano LC (nanoLC) to enhance the overall performance of the IT-SPME, the chromatographic separation, and the detection. Different monolithic polymers, such as silica C18 and C8 polymers, molecularly imprinted polymers (MIPs), polymers functionalized with antibodies, and polymers reinforced with different types of carbon nanotubes, metal, and metal oxide nanoparticles (including magnetic nanoparticles), and restricted access materials (RAMs) will be presented and critically discussed.

Low Pressure CO2 Capture with Amide-Based Imprinted Polymers

Bulk polymerization was used to fabricate molecularly imprinted polymer (MIP) adsorbents inherent with amine-functionality for post combustion CO2 capture. Polymerization was performed at 333 K for 24 hours using methacrylamide and ethylene glycol dimethacrylate (EGDMA) as the functional monomer and cross linker respectively, oxalic acid as the template azobisisobutyronitrile (AIBN) as the initiator and 4:1 (v/v) mixture of acetonitrile and dimethylformamide (DMF) as the porogenic solvent. The monolithic polymers were crushed and ground, followed by screening to 75-215 μm and the template was then removed from the polymeric particles by extraction using methanol and hydrochloric acid (90/10 v/v). A fixed bed adsorption column was used to investigate the performance of the dynamic CO2 uptake capacities. The X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FT-IR) spectra showed a huge number of -NH2 functionality distributed on the surface of the adsorbents, which thus enhanced the CO2 adsorption uptake. The maximum CO2 capture capacity was found in the MIP with the maximum template concentration (0.40 mmol/g, SBET 258 m2/g at 0.15 bar partial pressure and temperature of 313 K). The MIPs were stable thermally up to 518 K and the isotherms displayed type II revealing a non-uniform distribution of the pore size.

Hexavalent chromium removal performance of anionic functionalized monolithic polymers: column adsorption, regeneration and modelling

Anionic functionalized monolithic macro-porous polymers were used for the removal of hexavalent chromium(VI) anions from aqueous solution in column experiments. At a flux of 1.0 cm min and 30 mg Cr(VI) L−1 feed concentration, breakthrough capacity and apparent capacity were 0.066 g Cr(VI) g−1 anionic monolith and 0.144 g Cr(VI) g−1 anionic monolith, respectively. The degree of column utilization was found to lie in the range 41–46%. Two kinetic models, theoretical and Thomas models, were applied to experimental data to predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design. The simulation of the whole breakthrough curve was effective with the models. At a flux of 1.0 cm min and 30 mg Cr(VI) L−1 feed concentration, the dispersion coefficient and adsorption equilibrium constant (K) were 3.14 × 10−7 m s−1 and 3,840, respectively. Also, Thomas model parameters k1 (rate constant of adsorption) and qm (equilibrium solid-phase concentration of sorbed solute) were 1.08 × 10−3 L mg−1 min−1 and 0.124 g g−1, respectively. After reaching equilibrium adsorption capacity, the monoliths were regenerated using 1 N HCl and were subsequently re-tested. It was found that the regeneration efficiency reduced from 98% after second usage to 97% after the third usage.

Dual stereocontrolled alkylation of aldehydes with polystyrene-supported nickel complexes derived from α-amino amides

Nickel(ii) complexes derived from α-amino amide ligands anchored to gel-type and monolithic polymers act as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes.