Microextraction Tech

Zinc oxide has been used as coating in solid phase microextraction (SPME) due to its good properties including thermal stability and affinity towards different analytes. In this sense, ZnO presents a high interaction with sulfur-containing molecules due to the strong coordination between Zn and S. However, this interaction is not completely exploited in SPME since pure ZnO coatings, prepared by sol-gel procedures, have a low surface area due to the enwrapping of ZnO nanoparticles (NPs) in the sol-gel network. In a recent article accepted for publication in Journal of Chromatography A, researchers from the Sun Ya-sen University at China have proposed a new approach to avoid this shortcoming. The proposal consists of the use of graphene as ZnO NPs support. The ZnO NPs are grown in the graphene (G) surface producing a composite which is final attached to a silica fiber by a sol-gel reaction in order to prepare the SPME coating. The whole synthetic procedure is described in detai...

On-site solid phase extraction is specially indicated for those analytes which present a limited stability in the sample matrix. The procedure consists of the extraction of the sample immediately after its sampling and the final storage of the sorbent , containing the target analytes , until the final analysis which is usually performed in a conventional lab. Moreover, on-site extraction presents additional advantages in environmental analysis such as the simplification of the sample storage and transportation processes as only the sorbent with the extracted analytes has to be stocked up. The potential of stir bar sorptive extraction (SBSE) for the extraction of organic pollutants, especially for the most hydrophobic ones, from water samples is clearly demonstrated in the scientific literature. However, the applicability of the SBSE in on-site extraction is limited as it usually requires a large size magnetic stirrer powered by alternating current. This limitation has been face...

The fabrication of liquid chromatographic columns with variable interaction chemistry (dual, sequential or gradient composition) is a challenge issue although it presents a high potential for separation and extraction purposes. The direct packing of the stationary phase in a column, the usual way for homogeneous phases, results unpractical when heterogeneous materials are used. Moreover, the final stationary phase´ characterization becomes difficult since it should be performed directly on the stationary phase holder. In this context, the easy in-situ synthesis of monolithic materials makes them a good alternative of choice compared to classic phases. The easy derivatization of the monoliths is also a crucial aspect. In a recent article, accepted for publication in Microchemical Journal, Currivan et al. have proposed an acrylate-based monolith with integrated gold nanoparticles for the successive extraction and separation of target proteins in the same column (1). The proposed ...

Polymeric frits are employed in solid phase extraction to confine the sorbent in the cartridge avoiding it losses during the extraction procedure and to filter the sample avoiding the clogging of the cartridge due to the potential particulate matter present in the sample. Taking advantage of their organic nature -they are usually built with polyethylene- polymeric frits can be used as active sorbent allowing the retention of non polar analytes. Moreover, polymeric frits have been recently proposed as support for the synthesis of monolithic material (1) or molecularly imprinted polymers (2) for extraction purposes. Stir frit microextraction In a recent article, accepted for publication in Journal of Chromatography A, researchers from the University of Cordoba at Spain have proposed the use of polyethylene frits in the so-called stir frit microextraction technique (3). The new technique combines the extraction capability of this polymeric material with the stirring element, an ...

Carbon nanotubes reinforced hollow fiber microextraction (HF-SLPM) was proposed for the first time by Es´haghi et al. in 2010 (1). The original technique consisted of a multi-phase system where the aqueous donor and acceptor phases were separated by a polymeric membrane with a dispersion of carbon nanotubes in 1-octanol immobilized in its pores. The pH gradient established at both sides of the reinforced hollow membrane allowed the extraction of the target analytes. Due to its multiphase nature,  HF-SLPM  involves a selectivity enhancement compared to traditional hollow fiber liquid phase microextraction. Diethylstilbestrol The direct immobilization of carbon nanotubes (CNTs) in the pores of a polypropylene hollow fiber have been recently proposed by researchers from the Chinese Academy of Sciences of Beijing at China (2), for the isolation and preconcentration of diethylstilbestrol from milk. Diethylstilbestrol is a steroid hormone used for animal growth and it pre...

In the last decade, earthquakes have hit throughout the globe producing over 200.000 deaths (1). The effect of an earthquake depends  not only  on its size but also on the vulnerability of the buildings and infrastructure. In fact, a considerable percentage of deaths occur as a consequence of the building collapsing. In this context, the location of trapped victims becomes critical since their survival rate diminishes exponentially over the time. This location is usually performed by expert trained dogs as canine can analyzed large areas with high sensitivity. However, in the last years different instrumental techniques, such as ion mobility spectrometry (IMS), have been evaluated as alternative or complementary tools to canine work. In order to develop an efficient instrumental technique for the detection of human presence, two main aspects have to be considered. On the one hand, the selection of the biomarkers, as well as their biological source, is essential. In this s...

The efficient dispersion of the extracting phase into the sample is a useful strategy to enhance the kinetic of a given extraction technique. The dispersion enhances the contact area between phases making easier the transference of the target analytes across the interface. Dispersive procedures have been exploited both in the liquid and solid (micro)extraction techniques, being dispersive liquid-liquid microextraction (DLLME) a preeminent example. In DLLME, the dispersion of the extractant can be assisted chemically, by using a disperser solvent or surfactants, or applying an external energy source like ultrasounds. In a recent article, accepted for publication in Talanta, aerosol phase extraction (APE) has been proposed for the first time as an alternative to these conventional approaches (1). In APE the sample is nebulized by an inert gas into the extracting phase in the form of very small drops. APE presents two very positive aspects which must be highlighted. On the one han...

Stir cake sorptive extraction (SCSE) was proposed in 2011 by researchers from the Xiamen University at China as an alternative to classic stir bar sorptive extraction.(1) The novel extraction technique is especially useful when monolithic polymers, characterized by their low mechanical stability, are employed as extracting phases. In SCSE a disk of monolithic material is introduced in a dedicated device in order to protect it from cracking due to the friction with the extraction vessel walls. The device also allows the stirring of the solution, thanks to a metallic wire, enhancing the analytes transference from the bulk solution to the extracting phase. In the first application, the efficient extraction of steroid hormones from milk was achieved using poly(vinylimidazole-divinylbenzene) monolithic with a low effect of the sample matrix (it was not required to remove fat and proteins). In a recent article, accepted for publication in Journal of Chromatography A, the same research ...

Single drop microextraction (SDME), which was described in the middle 90´s, is an effective extraction technique which comprises isolation and preconcentration in one step, allowing the direct injection of the extracts in different analytical instruments. In SDME, a small volume of extractant is aspirated in a microsyringe which is introduced in the extraction vessel where the sample is located. A small drop of extractant, in the range of 1-5 µL, is finally exposed to the sample (direct immersion mode) or to its headspace (headspace mode) in order to extract the target analytes. After the extraction, the drop is retracted into the microsyringe which will be finally transferred to the appropriate analytical instrument. In the usual situation, the extractant is an organic solvent with suitable properties. In this way, the solvent should present a high affinity towards the analytes in order to isolate them from the sample matrix. Moreover, the organic solvent should present a low vo...

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...