Microextraction Tech

Electromembrane extraction (EME) is a liquid phase microextraction technique based on the voltage-assisted migration of the target analytes between two aqueous solutions (the sample and the acceptor phase) separated by a polymeric membrane where an organic solvent is immobilized in the form of a supported liquid membrane (SLM). The technique, which has been the subject of several posts in this blog, allows the rapid extraction of ionic species. The present post highlights a recent article, published in the Journal of Pharmaceutical and Biomedical Analysis, where polyacrylamide gels are proposed as a membrane in EME. Although polypropylene membranes are usually selected as a physical barrier between the two aqueous phases involved in EME, several research groups have proposed alternatives to this classical approach. In 2017, Tabani et al. proposed agarose gel as a greener alternative. Although good results were obtained, the large pore sizes of these gels (up to 300 nm) ...

Membranes can be used for different purposes in Analytical Chemistry. In the extraction context, they permit the development of several liquid-liquid extraction techniques such as dialysis, osmosis, among others. Also, they can provide an additional enhancement of the selectivity by the direct selection of the pore size. They are also commercialized in different formats (planar, tubular) and polarities in such a way that they can be applied to almost any analyte-sample binomial. In liquid phase microextraction, membranes have been used under the 2 phases and 3 phases formats depending on the number, nature and role played by the different liquid phases involved. In order to favor the kinetic of the whole process the continuous agitation of the system is recommended to accelerate the diffusive transport of the target compounds in both the donor and acceptor phases reducing the thickness of the diffusion layer near the membrane. Prof. Dr March and Prof. Dr. Cerdá have recently pro...

Today, we focus the attention on an interesting article recently published in Journal of Chromatography A by researchers from the University of Tasmania at Australia. As our readers well known, electrodriven liquid microextraction techniques present a high efficiency for the extraction of charged analytes. In those techniques, the analytes migrate from the sample to the acceptor phase as a consequence of the voltage gradient established between both phases. In the off-line modes, the involved phases are often physically separated by an organic phase or a polymeric membrane impregnated with an appropriate organic solvent. Our colleagues have proposed a novel configuration that permits the development of the extraction procedure without any physical barrier between phases (1). The device consists of a 20 µL micropipette (a microtube with length of 6.4 cm and inner diameter of 0.3 mm) where the acceptor phase is located. The upper part of the microtube is introduced into a syringe th...

The article that we highlight today describes a new, simple, efficient and automated extraction technique for high throughput bioanalysis. It has been published in Analytical Chemistry under the title " Gas Pressure Assisted Microliquid–Liquid Extraction Coupled Online to Direct Infusion Mass Spectrometry: A New Automated Screening Platform for Bioanalysis" (1). It is interesting to note that we have described another article from the same research group in a previous post ( Three phase electroextraction ). According to the title, Gas Pressure Assisted Microliquid–Liquid Extraction (GPA-µLLE) is based on the thorough mixture of an aqueous biological sample (donor phase) and a organic solvent (acceptor phase) by means of a gas stream. However, the potential of this technique goes beyond this simple description for many reasons, among which the following are of note : The technique is developed in a multi-plate platform and therefore it can process a high number of s...

Analytica Chimica Acta (ACA) has published a novel analytical method which combines extraction and clean-up in a single step. The so-called salting out supported liquid extraction (SOSLE) follows the liquid-liquid extraction principles, its main advantage being the capability of extracting compounds of a wide polarity range (1). The technique was evaluated using the multi-residue quantification of veterinary drugs in milk as model analytical problem. Acetonitrile was selected as extractant and the immiscibility with the aqueous sample is achieved by using a high concentration of ammonium sulfate, thus permitting the supported liquid-liquid extraction (SLE) using a polar organic solvent. The benefits of SLE technique has been recognized  by Ronald E. Majors, editor of "Sample Preparation Perspectives" in LC/GC journal, who defined it as the best kept secret in sample preparation (2). The approach presented in ACA by our colleagues from Zurich overcomes the limitation of c...

In a recent article published in Analytical Methods, researchers from the Shanxi Medical University at China have presented a novel microextraction approach for the determination of flavanoids and anthraquinones from traditional Chinese herbs. The authors use two different organic solvents placed in two filter membranes as extraction device. The main advantage of the so-called multiple-solvent simultaneous microextraction (MSSME) are the wide exchange surface and the selective extraction provided by the organic solvents used. The miniaturized extraction unit (see Figure) was constructed as follows. Two square pieces (1cm X 1cm) of filter membrane were separately immersed in 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF 6 ]) and decanol for 10 s. In this way, the pores of the membrane are impregnated with the extractants. The excess of the solvents was removed using absorbent paper. Once prepared, the solvent impregnated membranes were pierced by a microsyringe needle...

In 2011 a new sample pre-treatment technique, called Effervescence-assisted dispersive micro-solid phase extraction, was proposed. The technique was based on the use of an effervescent reaction (reaction between a proton donor and a carbonate source releasing gaseous CO 2 ) for the efficient dispersion of a sorbent. For this purpose a lab-made effervescent tablet, containing all the reagents necessaries to perform the dispersive extraction (NaH 2 PO 4 ) as proton donor, Na 2 CO 3 as carbonate source and the appropriate sorbent) is directly added to the sample. The tablet, which is 250 mg in weight and 102 mm in diameter, is produced by the simple blending of the precursors and their final compression in a hydraulic manual press. The final tablets are stable enough if they are stored under inert atmosphere to preserve them from the environmental humidity, which reduces the CO 2 releasing potential and dispersion efficiency. The tablet composition is optimized considering the effe...

In March we published a post about electromembrane extraction  (EME), which was firstly proposed in 2006 by Pedersen-Bjergaard and Rasmussen. This microextraction technique is based on the voltage-assisted migration of the target analytes from two aqueous solutions, the sample and the acceptor phase, which are separated by a polymeric membrane where an organic solvent is immobilized in the form of a supported liquid membrane (SLM). Recently, a research group of the University of Leiden at Netherlands has presented a three phase electroextraction technique that shares some of the principles of EME. The new technique is characterized by the extreme reduction of the required sample and extractant volumes and therefore it is especially interesting for bioanalytical applications. Moreover, the process is rapid and it has been coupled on line to nanoelectrospray direct infusion mass spectrometry. The proposed manifold is schematically described in the Figure. 50 µL of an aqueous...

The extraction of polar and/or metal traces from oily samples is an analytical challenging task due to the nature of the sample matrix. Casella et al. proposed, in 2010, the extraction induced by emulsion breaking technique which faced up this challenge with high success (1). This technique is based on the formation of a stable emulsion between the oily sample (diesel, oil etc.) and an aqueous phase that contains a surfactant. The surfactant promotes the emulsification of both phases favoring their contact and therefore, making easier the transference of the analytes from the non-polar to the polar phase. After the extraction, the emulsion should be broken, usually by centrifugation, in order to allow phase’s separation and the final analysis of the aqueous phase. In a recent article, accepted for publication in Talanta, the same authors have proposed a similar approach for the determination of Cu, Fe and Mn in used lubricating oils (2). This determination is quite important si...

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...

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...

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...