Microextraction Tech

A new microextraction approach which stands midway between solid phase microextraction (SPME) and single drop microextraction (SDME) has been recently reported by researchers of the University of Isfahan at Iran. The extraction device is quite similar to this employed in SPME, although a bare stainless steel wire is used instead of the classic fiber. The wire is chemically treated in order to anchor a nanolayer of silica on its surface. This synthesis is achieved by a hydrothermal reaction which simply consists on the immersion of the bare wire in a sodium hydroxide solution in close contact with a glass precursor. The reaction, which develops at high temperature, involves the dissolution of the glass precursor in the alkaline solution and its final deposition on the wire. As a result of the process, a microporous layer of silica with a thickness of ca. 14 µm is obtained in the surface of the metallic wire. For analytes extraction, the treated wire is immersed in an appropriate org...

Researchers from the University of Bialystok at Poland have reported an extraction procedure which uses immobilized microorganisms as active sorbent for the isolation and preconcentration of platinum from water samples. The article, recently published in Microchimica Acta, describes the on-line combination of the extraction step with the final chemiluminescent determination of the target analyte using a flow injection manifold. Biomass sorbents based on different microorganisms have been extensively used in inorganic chemical analysis since the cell walls present interaction sites towards metallic ions. These sites present different interaction mechanisms such as ionic exchange, physical adsorption, complexation or microprecipitation. The type of interaction directly depends on the chemical composition of the cell wall, which is characteristic of each microorganism. In this case, the authors proposed a filamentous fungus (Aspergillus sp) which presents a polysaccharide rich wal...

The presence of fragrances in cosmetics could be a problem of health concern, since some of the employed chemicals may induce asthma, migraines headaches and other adverse effects. In fact, the European Union has established a list of 26 potential allergens used as fragrances, 23 of them being volatiles terpenes. These substances may act also at low concentrations and therefore their analytical monitoring is desirable, even in theoretically fragrance-free products. Researchers from the University of Vigo (Spain) have recently presented in a research article, published in Analytica Chimica Acta, a rapid screening method for terpenes in cosmetics. This approach is based on the potential fluorescence quenching that these hydrophobic compounds induce in the bovine serum albumin (BSA)- fluorescein (F) system. The potential quenching effect of terpenes in BSA-fluorescent indicator systems is well reported in the literature. However, this general approach does not allow the determinati...

Molecularly imprinted polymers (MIPs) can be defined as polymeric networks with selective cavities towards an analyte or structural-related substances. MIPs present some advantages over their natural counterparts, the immunosorbents, since they present higher stability and reusability. Moreover, MIPs can be easily tuned depending on the target analytes. The latter aspect is a consequence of the synthetic process which simply consists on the creation of the polymer in the presence of the target analyte which acts as template of the polymeric network. After the synthesis, the template is conveniently removed leaving cavities with an enhanced selectivity towards the analyte. This synthetic procedure can be easily applied to a wide variety of organic compounds but it presents an obvious limitation when biomolecules, like proteins, are processed. In fact the three-dimensional structure of proteins, which is essential in their activity, is instable in the reaction media or it can be af...

Cigarette filters (CFs) are employed to reduce the amount of smoke and toxic substances (tar and particulate matter) inhaled during smoking. Commercial filters usually consist on a large number of cellulose acetate fibers which act as particulate sieves as well as contaminant traps. The latter aspect, based on the chemical interaction of CFs with different organic substances, permits their use as sorptive phase in solid phase extraction (SPE). The first application of CFs in this context was published by Yan et al. in 2003 for the determination of traces of methylmercury by electrothermal atomic absorption spectrometry (ETAAS).

Polymeric nanofibers present high surface-to-volume ratios which make them so attractive in extraction procedures since their high superficial area increases the potential interaction analyte-sorbent with positive thermodynamic and kinetic connotations. The synthesis and preparation of these nanofibers can be achieved in the lab by electrospinning. This process is based on the application of a high voltage to a polymer solution in order to produce a thin liquid jet which is finally ejected. First of all, a precursor of the nanofiber polymer is dissolved in an appropriate solvent to produce a viscose solution which is introduced in a syringe for its dispensation at a fixed and controlled velocity. Later on, an electric field (high voltage) is established between the syringe needle and a collector which acts also as the receptor of the produced nanofibers. As a consequence of this electric field, the mutual charge repulsion on the surface of the liquid overcomes the surface tension...

Single drop microextraction (SDME) can be considered the first technique in the liquid phase microextraction context. It is a simple procedure which involves sampling and injection in the same device in a similar way to solid phase microextraction. In this case, a small drop (usually in the range from 1 to 5 µL) is suspended in the needle of a microsyringe which is immersed in the sample or kept into close contact with its headspace. Single drop-based microextractions usually present problems derived from the instability of the drop which results in its detachment when volumes higher than 5 µL are employed. This limitation has also a clear influence in the absolute recovery of the extraction technique and it may restrict its coupling with liquid chromatography where higher injection volumes are required. In 2006, Lu et al. presented the so-called directly suspended droplet microextraction (DSDME) which overcame some of these limitations. This single drop-based technique consists...

Electromembrane extraction (EME), which was firstly proposed in 2006 by Pedersen-Bjergaard and Rasmussen, is based on the voltage-assisted migration of the target analytes from two aqueous solutions: the sample and the acceptor phase. Both phases are separated by a polymeric membrane where an organic solvent is immobilized in the form of a supported liquid membrane (SLM). EME shares some of the principles and a similar manifold that this employed for hollow fiber-liquid phase microextraction (HF-LPME). As it is schematized in the Figure, the sample is located in an appropriate vessel where a polypropylene hollow fiber (HF) is introduced. The HF contains the acceptor phase in the lumen and an organic solvent in the internal pores acting as a physical barrier between the two aqueous solutions. Moreover, the EME manifold involves two electrodes which are located in the sample and the HF lumen, respectively. The voltage applied between both electrodes is the driving force of this ext...

Carbon-based nanomaterials have been extensively used as coatings in solid phase microextraction (SPME) due to their outstanding properties such as high thermal and mechanical stability, large superficial area and high affinity towards different compounds. Graphene (G), which was discovered in 2004, consists of one-atom-thick planar sheets of sp 2 -bonded carbon atoms that are densely packed in a honeycomb crystal lattice (see Figure). It can be considered the building block of some carbon allotropes like carbon nanotubes or graphite. In fact, in the usual synthetic procedure, graphene is obtained in the form of graphene oxide (GO) by chemical exfoliation of graphite. This GO can be finally reduced to G using reagents (like hydrazine or p -phenylene diamine) or a thermal treatment.

The usefulness of sorptive microextraction approaches, like solid phase microextraction (SPME) or stir bar sorptive extraction (SBSE), in the isolation and preconcentration of organic pollutants from water is well established in the scientific literature. Classic SPME or SBSE are mainly focused on the extraction of non-polar compounds since the typical coating, polydimethlysiloxane (PDMS), is hydrophobic. While the main pollutants considered 20 years ago had a hydrophobic nature, most of the emerging contaminants present a medium to high polarity. Therefore, new sorptive phases are desirable in order to extend the scope of these extraction techniques.

We recover today an interesting article published a few months ago in the International Journal of Astrobiology. The search for life (or trace remains of it) in Mars is still discussed in the scientific community. In this sense, organic molecules can be considered as tracers of a potential existing life or extinct life. However, the extreme conditions of Mars surface (UV solar radiation, for example) are not the best environment to preserve these organic molecules. Polycyclic aromatic hydrocarbons (PAHs), which are ubiquitous in the solar system, are especially resistant to these hard conditions. In fact, PAHs have been detected in meteorites. In this article, the authors evaluated the potential of solid phase microextraction (SPME) under its headspace (HS) mode for the extraction of PAHs in Mars analogue soil samples. The final identification and determination of the extracted analytes are achieved by means of gas chromatography-mass spectrometry. Soil obtained near to Mars Dessert ...

The term “nanoparticle” (NP) involves a great variety of materials. According to the size, a NP can be defined as a particle that presents one or more dimensions in the nanometer range, considering 100 nm as arbitrary reference. However, the prefix “nano” also refers to the novel physical and chemical properties that appear in the nano-scale. In the microextraction context, NPs are attractive due to their high superficial area which improve the extraction kinetics. Moreover, in most of the cases, NPs are easily synthesized and they can be derivatized in-surface providing different interaction chemistries. However, the management of these NPs is rather complicated in classic SPE since their small particle size and aggregation tendency usually produce back-pressures in the extraction devices.