A critical retrospective and prospective review of designs and materials in in-line solid-phase extraction capillary electrophoresis

Several strategies have been developed to decrease the concentration limits of detection (LODs) in capillary electrophoresis (CE). Nowadays, chromatographic-based preconcentration using a microcartridge integrated in the separation capillary for in-line solid-phase extraction capillary electrophoresis (SPE-CE) is one of the best alternatives for high throughput and reproducible sample clean-up and analyte preconcentration. This review covers different designs (geometrical configurations, with frits or fritless, capillary types, compatibility with commercial instrumentation, etc.) and materials (sorbents, supports, affinity ligands, etc.) applied for almost 30 years to prepare in-line SPE-CE microcartridges (i.e. analyte concentrators), with emphasis on the conventional unidirectional configuration in capillary format. Advantages, disadvantages and future perspectives are analyzed in detail to provide the reader a wide overview about the great potential of this technique to enhance sensitivity and address trace analysis.

The influence of amine structures on the stability and catalytic activity of gold nanoparticles stabilized by amine-modified hyperbranched polymers

Amine-modified amphiphilic hyperbranched polymers (MePEG-H104-Nx) were prepared from hyperbranched 2,2-bis(methylol)propionic acid polyester (H104) by decoration with polyethylene glycol monomethyl ether (MePEG) and different classes of oligo(ethylenimine)s. By using the MePEG-H104-Nx polymers as stabilizers, gold nanoparticles (AuNPs) were prepared in an aqueous medium by the reduction of HAuCl₄ with NaBH₄. The AuNPs were sphere-like with diameters of 2-4 nm, which were dependent on the structure of the amines. Further, the catalytic activity of these AuNPs was evaluated by monitoring the reduction reaction of 4-nitrophenol by sodium borohydride. The results demonstrate that the longer chain length and the branched structure of the amine moieties are beneficial for the stability and catalytic activity of the AuNPs. The AuNPs stabilized by MePEG-H104-N4 and MePEG-H104-Nb3 showed high catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol.