Microextraction Tech

Figure 1. Structure of SWCHs Carbon allotropes have been extensively used as sorbents in solid phase extraction (SPE) and solid phase microextraction (SPME). Graphitized and activated carbons, fullerenes, carbon nanotubes, diamond and graphene can be highlighted among this class of materials. Today we focus our attention on the potential of carbon nanohorns as sorbent in SPE. Single walled carbon nanohorns (SWCNHs), which were discovered by Ijima in 1999, are single wall graphitic structures formed out of a single graphene sheet rolled up to form conical (horn-like) shapes which are rounded at the tip (1). These nanoparticles, schematically presented in Figure 1, tend to aggregate producing dahlia-like structures with sizes in the range from 80-100 nm. Thanks to their high superficial area and their ability to interact with different analytes, SWCNHs can be considered as promising nanomaterials in extraction procedures (2). Moreover, the weak interaction between individua...

Dispersive liquid-liquid microextraction (DLLME) was firstly proposed by Rezaee et al. in 2006 (1) as a simple, rapid and cheap extraction technique capable to provide high recoveries and enrichment factors. In DLLME, the organic acceptor phase is dispersed into the sample assisted by an appropriate solvent or by an external energy source (like ultrasounds) producing a cloudy solution. As a consequence of the dispersion, the surface to volume ratio of the acceptor phase increases dramatically, making easier the mass transference through the interfase and therefore reducing the extraction times and increasing the enrichment factors. After the dispersion, the organic extractant should be recovered for its final analysis. This final step is the limiting factor of the technique since in most of the cases a centrifugation step is required. Despite its efficiency, the centrifugation step is an off-line process which avoids the potential automation of the technique and therefore its integra...

Restricted access materials (RAMs) are sorbents with enhanced selectivity due to their inherent structure since their extractive groups are protected by external functional groups that exclude macromolecules by a size exclusion and/or an electrostatic repulsion mechanism. Thus, only the small target analytes are able to reach the extracting phase avoiding the clogging of the sorbent by the sample matrix. In a recent article accepted for publication in Journal of Chromatography A (1), researchers from Wuhan at China have proposed a new RAM based on the combination of magnetic nanoparticles and non-ionic surfactants. Magnetite nanoparticles (Fe304), which are synthesized by an oxidative-coprecipitation method, are the core of these RAMs providing them with a paramagnetic behavior which is essential for their easy isolation after the extraction process. The magnetite particles, with sizes in the low nm range, are subsequently derivatized with dodecyltriethoxisilane anchoring C12 ext...

Electrochemically controlled solid phase microextraction (EC-SPME) was proposed as an alternative to classic SPME for the enhanced isolation of ionic or ionizable compounds (1). EC-SPME is based on the application of a potential difference between the sample and the extracting phase, and therefore special conducting coatings, such as those based on polypyrrole, are required. Classic SPME coatings lack of extraction selectivity due to their hydrophobic nature. As we've mentioned in previous posts (I, II), molecularly imprinted polymers enhance the recognition selectivity through hydrogen-bonds, ionic interaction, and size-shape matching. In a recent article, published in Analytica Chimica Acta, Liu et al. have proposed a nanocomposite as special coating in EC-SPME for the selective extraction of fluoroquinolones from water samples (2). The nanocomposite is based on the combination of carbon nanotubes (CNTs), which increase the stability and mechanical strength of the fiber, a...

Inside needle capillary microextraction (INCAT) is a promising solid phase microextraction (SPME) mode where the sorbent material is immobilized in the inner walls of a hollow stainless steel needle allowing the continuous sample flow through the extracting phase. Therefore, INCAT enhances the kinetic of the extractions and improves the preconcentration factors since larger sample volumes can be processed. Moreover, the extraction device is inexpensive, robust and it presents a higher mechanical stability compared to classic SPME fibers. Although conventional SPME materials can be employed as extracting phases in INCAT, new materials have been developed in this context. Bagher at al. have already described, in a research article published in the Journal of Separation Science, a nanocomposite for the extraction of polycyclic aromatic hydrocarbons in water (1). The nanocomposite is based on the combination of hexagonally ordered silica (SBA-15) and polyaniline, each component pl...