Microextraction Tech

The efficiency of a given microextraction technique depends on both thermodynamic and kinetic aspects. The distribution constant defines the maximum extractable analyte whereas the kinetic establishes the rate at which this distribution takes place. Among the kinetic factors, the efficient diffusion of the target analytes from the bulk sample solution to the acceptor phase is a key aspect. This diffusion can be easily enhanced by an efficient stirring of the sample or the acceptor phase during the extraction. Solvent bar microextraction (SBME), which was firstly presented by Jiang and Lee in 2004, (1) enhances the diffusion of the analytes through an efficient stirring of the acceptor phase. SBME uses a solvent immobilized in the lumen and pores of a polypropylene hollow fiber as extracting phase. Both ends of the hollow fiber are sealed and the resulting solvent bar is introduced in the sample where it moves free and randomly. After the extraction, the solvent bar is recovered a...

Zinc oxide (ZnO) nanoparticles have been successfully employed in different application fields due to their inherent characteristics such as wide band-gap or thermal stability. As with other nanomaterials, zinc oxide may exist in many structural forms depending on the synthetic process. In this sense, ZnO nanorods can be easily obtained in the laboratory by a hydrothermal treatment using zinc nitrate and hexamethylenetetramine as precursors. The concentrations of the precursors, as well as the temperature and incubation time, play a key role in the final physical characteristics of the product as it is indicated in Figure 1. Figure 1A shows a scanning electron micrograph of the ZnO nanoparticles before the hydrothermal reaction while Figures 1B-C illustrate the final product using different starting equimolar concentrations of the precursors (0.1 mM, 1mM and 10 mM, respectively). The average width and length of the nanorods increase with the initial concentration of precursors. H...

The direct application of molecularly imprinted polymers (MIPs) for the selective recognition and isolation of proteins has some limitations. As we described in a recent post , the tridimensional structure of the protein can be modified during the MIP synthesis due to the solvents or the monomers employed. On the other hand, the huge molecular size of biomolecules restricts their diffusion through the polymeric network making difficult their extraction and/or final elution. Smart hydrogels can substitute conventional polymeric materials in molecularly imprinting due to their peculiar characteristics. A smart hydrogel is a porous polymeric network that may respond to external stimulus (mainly pH, ionic strength or temperature) with a change in its structure or dimension. This change can be used to control the uptake and release of the templates with a negligible effect on the polymeric network which memorizes the imprinting state. This polymeric network is synthesized using thre...

Figure 1. Structure of polythiophene Despite their potential, the applicability of polythiophene (PT) based coatings in solid phase microextraction (SPME) is limited by their low thermal stability. In fact, PT coatings are not suitable for temperatures higher than 200 ºC and therefore they are not applicable for the extraction of a wide variety of semi-volatiles analytes. Moreover, the use of low desorption temperatures usually causes carry-over problems as the analytes are not effectively desorbed between two consecutive extractions. The improvement of the thermal stability of PT can be achieved by two different strategies which consist in the addition to the polymerization mixture of dopants with negatively charged groups. In the first approach, special reagents (like surfactants) are directly added to the polymerization mixture while in the second approach special monomers containing negative charged moieties are used to produce the so-called self-doped polymers. The l...

Carbon nanotubes (CNTs) have been extensively used for the solid phase extraction (SPE) of a great variety of compounds including not only hydrophobic molecules but also polar analytes and metal ions. This versatility is based on the easy chemical modification of the nanotubes which allows the introduction of functional groups that enhance the interaction with the target analytes. The functionalization of the CNTs is usually started with the introduction of oxygen-containing groups such as carboxyl (-COOH) or hydroxyl (-OH) ones, that are further transformed in the desired moieties. However, this general process requires the use of extreme oxidation conditions which may eventually produce the CNT shortening as well as defects on the CNT surface. In a recent communication, researchers from the Tongji University at China use the radical addition with aryl diazonium salts to introduce functional groups in CNTs surface under mild conditions. In fact, the reaction can be easily pe...