Abstract
The extraction yield of a microextraction technique depends on thermodynamic and kinetics factors. Both of these factors have been the focus of intensive research in the last few years. The extraction yield can be increased by synthesizing and using novel materials with favorable distribution constants (one of the thermodynamic factors) for target analytes. The extraction yield can also be increased by improving kinetic factors, for example, by developing new extraction modes. Microextraction techniques are usually non-exhaustive processes that work under the kinetic range. In such conditions, the improvement of the extraction kinetics necessarily improves the performance. Since the extraction yield and efficiency is related to how fast the analytes diffuse in samples, it is crucial to stir the sample during extraction. The stirring can be done with an external element or can be integrated with the extraction element in the same device. This article reviews the main recent advances in the so-called extraction/stirring integrated techniques with emphasis on their potential and promising approaches rather than in their applications.
Highlights
Microextraction techniques are physicochemical processes based on the mass transference between, at least, two different phases
This phenomenon is behind the development of dispersive techniques [2] where the liquid or solid extractant is dispersed in the form of fine droplets or small-sized particles into the sample
Logue et al have proposed the so-called ice concentration linked with an extractive stirrer (ICECLES) which combines the advantages of freeze concentration and Stir bar sorptive extraction (SBSE) [28]
Summary
Microextraction techniques are physicochemical processes based on the mass transference between, at least, two different phases. Microextraction techniques usually work under diffusion controlled conditions This situation, a direct consequence of the size difference between the sample and extractant phases (the diffusion paths of the analytes become larger), is of paramount practical importance. The thickness of the boundary layer between the bulk sample and extractant affects the extraction rate. Some techniques are based on the integration of the agitation and extraction elements in the same device This integration simplifies the extraction to a large extent, avoids analyte losses due to retention on external devices, and enhances the extraction yields. These techniques, that can be named as extraction/stirring integrated techniques, are the topic of this review article. This contribution reviews the recent developments of these techniques rather than focusing on the applications reported in the field
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