Stir frit microextraction

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Polymeric frits are employed in solid phase extraction to confine the sorbent in the cartridge avoiding it losses during the extraction procedure and to filter the sample avoiding the clogging of the cartridge due to the potential particulate matter present in the sample. Taking advantage of their organic nature -they are usually built with polyethylene- polymeric frits can be used as active sorbent allowing the retention of non polar analytes. Moreover, polymeric frits have been recently proposed as support for the synthesis of monolithic material (1) or molecularly imprinted polymers (2) for extraction purposes.

Stir frit microextraction
In a recent article, accepted for publication in Journal of Chromatography A, researchers from the University of Cordoba at Spain have proposed the use of polyethylene frits in the so-called stir frit microextraction technique (3). The new technique combines the extraction capability of this polymeric material with the stirring element, an iron wire. The new proposal has been evaluated determining single ring aromatic hydrocarbons (benzene, toluene, xylenes, ethybenzene and styrene) in waters by gas chromatography-mass spectrometry.

The optimized analytical methodology combines two different extraction modes. First of all, the target analytes are isolated from a large volume of water (100 mL) by means of the stir frit microextraction technique. Once the analytes are isolated, the frit is transferred to a glass vial where a headspace analysis takes place. The combination of both procedures enhances the selectivity of the method since only non-polar volatile compounds can reach the gas chromatograph. However, the authors admit that the headspace step limits the potential sensitivity enhancement as it involves a dilution of the analytes immediately before their determination. In fact, if we consider only the stir frit microextraction step, preconcentration factors (PFs) in the range from 157-998 can be obtained. Moreover, there is a clear relationship between the PFs and the analytes hidrophobicity.

The readers are referred to the original article where they will find a deeper discussion of the results, including the optimization of the proposal and its analytical characterization.

References:

(1) A novel solid-phase microextraction method based on polymer monolith frit combining with high-performance liquid chromatography for determination of aldehydes in biological samples. Link
(2) Molecularly imprinted polymer grafted to porous polyethylene frits: A new selective solid-phase extraction format. Link
(3) Stir frit microextraction: an approach for the determination of volatile compounds in water by  headspace- gas chromatography/mass spectrometry. Link

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