Microextraction Tech

The use of nylon membranes modified with carbon nanotubes (CNTs) for the determination of caffeine in biological fluids has been proposed by researchers from San Luis University at Argentina (1). The proposed configuration is based on the retention of the analyte into the modified membrane and its in-surface determination by means of solid surface fluorescence (SSF). Although caffeine is not a fluorescent molecule, this methodology takes advantage of the interaction between caffeine and Rhodamine B which produces an enhancement of the native fluorescence of this dye.   (a) Rhodamine B   (b) Caffeine Modified membranes are easily fabricated by impregnation of the bare membranes with a solution that contains Rhodamine B, activated CNTs and hexadecyltrimethylammonium bromide (HTAB), the latter being a cationic surfactant employed for CNTs dispersion. After a drying step the membranes are ready to isolate caffeine from biological samples. The extraction procedure makes us...

High surface solid phase microextraction (HSA-SPME) is an interesting extraction technique developed in 2009 which enhances the efficiency of classic SPME by increasing the total area of the extracting phase (1). The core of the classical HSA-SPME device is an oxidation-resistant metallic wire coated with a carboxen/polydimethyl siloxane film which is the responsible for analyte extraction. This metallic wire is wrapped around a borosilicate glass tube which is introduced in an outer glass tube where a gaseous sample flows in a controlled fashion (see Figure 1).   Figure 1. High surface solid phase microextraction device HSA-SPME consists of two general steps. First of all, a gaseous sample is introduced into the device at a controlled flow and the analytes are retained in the SPME coating. Once the sampling has been completed, the target analytes are thermally desorbed applying an electric current to the metallic wire and further focused and preconcentrated on a microtrap...

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...

Dispersive liquid-liquid microextraction (DLLME) is a consolidated technique in the treatment of liquid samples due to its rapidity and efficiency. In fact, the almost complete extraction of the analytes, with absolute recoveries near to 100%, can be achieved in a few minutes. In the classical DLLME approach a mixture of solvents, the disperser and extraction ones, is injected in the sample producing the efficient dispersion of the extractant which enhances the contact area with the sample. After dispersion, the extract is recovered by means of a centrifugation step. Despite its usefulness, the classical approach presents some limitations. For example, the requirement of a disperser solvent in the mL range is not completely compatible with a green procedure, although the typical solvents are not too toxic. Moreover, the disperser solvent may participate in the analytes partition, especially for polar analytes, increasing the solubility of the analytes in the sample. Air assist...

Solid phase extraction (SPE) is a consolidated technique in sample pretreatment thanks to its robustness, enrichment capacity and selectivity enhancement. The great variety of commercial sorbents covering a wide range of interaction mechanisms, as well as the development of novel materials makes SPE a very versatile technique. Despite its usefulness, classic SPE still presents some shortcomings such as the requirement of moderate to high sample volumes or the use of organic solvents in the milliliter range. These limitations have been faced up by different research groups and as a consequence of these efforts new techniques, for instance microextraction by packed sorbent or pipette tip extraction, have emerged. Pipette tip extraction is based on a simple but innovative idea which consists in placing the sorbent inside a pipette tip. This approach allows the handling of low sample volumes requiring also lower volumes of organic solvents in the elution step. The sorbent can be used...

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...

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...