Microextraction Tech

Single drop microextraction (SDME), the first liquid phase microextraction technique proposed, is a simple approach consisting of the extraction of the target analytes from the sample into a small drop of extractant. The characteristics of the drop, specially its chemical nature and mechanical stability, are key factors to guarantee the success of the extraction. Its chemical composition defines the affinity towards the target analytes which are, in fact, extracted depending on their solubility. The mechanical stability of the drop during the extraction is critical since the drop detachment would ruin the extraction. The drop volume and handling increase the probability of that detachment. Researchers from Ukraine and Slovak Republic have already published in Analytical Chemistry journal a nice contribution to SDME that overcomes this shortcoming(1). In this case, an optical probe is used as the drop holder in such a way that the continuous UV-Vis monitoring of the drop is achieve...

Miniaturization of classical extraction procedures, which was the origin of microextraction techniques, has reduced the consumption/requirement of extractant solvents in the liquid-based formats from the mL to the m L range. The use of lower droplets, at the nL or even pL levels, opens a door to process special systems characterized by their small sizes or low availability. In a previous post, we discussed the potential of liquid extraction surface analysis (LESA) [1,2]. This technique is so powerful to analyze surfaces as it integrates the liquid extraction of the solid samples with the on-line mass spectrometric (MS) analysis of the extracts. LESA works with nL droplets allowing the superficial analysis of tissues or bacteria colonies. One question arises in this context. Is it possible to use this technology to analyze single cells? For the theoretical point of view, that approach is possible. However, a recent study published in Nature points up that using nL droplets to ext...

The intentional incorporation of air bubbles to solvent drops enhances the extraction efficiency in single drop microextraction (SDME). The reason behind this experimental fact is simple: the air bubble increases the surface to volume ratio of the drop. In other words, the same organic solvent volume presents a larger surface and therefore a better extraction kinetics. This idea, which was firstly proposed by Williams et al. in 2011, [1] has been recently revisited by the same research group proposing mixed solvents as extractant. Mixed solvents can present even better extraction properties, due to special combination of physicochemical characteristics, than the individual solvents used in that mixture. In fact, our colleagues confirmed both aspects in a recent article published in Talanta [2]: According to the results, the enrichment factors obtained for the bubble in drop SDME (BID-SDME) are higher (ca. 1.5 times) than that obtained with the conventional SDME. The use of ...

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...

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...

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...