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...