Monitoring a single C18 particle by confocal Raman microscopy

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Solid phase extraction (SPE) is a consolidated sample treatment technique based on the retention of the target analytes in an appropriate sorbent thanks to different chemical interactions. SPE allows the enhancement of the selectivity and sensitivity of an analytical methodology through removing potential interferences and increasing the concentration of the target compounds. The latter depends directly on the extraction efficiency (defined as the absolute extraction recovery), as well as the volumes of the sample processed and the final eluent. Objectively seen, the final elution produces a dilution of the analyte which is previously confined in a lower amount/volume of the sorptive phase, thus reducing the potential enrichment factors of the technique.

Solid phase microextraction (SPME) faces up the "elution problem" with a clever strategy that consists on the elution of the analytes inside of the instrument. In this sense, the fiber with the extracted analytes is introduced in the injection port of a gas chromatograph (or in a dedicated interface in liquid chromatography) and the total amount of the extracted analyte is efficiently transferred to the instrument and measured.

The "elution problem" can be avoided if the elution is not performed, but.. how can that be?. This is made possible by the direct monitoring of the target analyte on sorbent particle. This strategy, which has been performed by different spectroscopic techniques, has been recently revisited by researchers of the Utah University (1). The article, which has been published in Analytical Chemistry, describes the determination of pyrene in a single chromatographic particle by confocal Raman microscopy. C18 silica particles (10 µm in size) are employed to extract the analyte from a methanol/water solution by hydrophobic interactions. The confocal Raman microscopy, which allows the monitoring of the particle interior where the analyte is retained, is employed to quantify pyrene using its characteristic Raman bands. In addition, the signal provided by the C18 chain is employed as internal standard in the measurements. The proposal has been employed to measure the isotherms of the analyte extraction.

From Microextraction Tech, we invite our followers to go through this article and check the really astonishing results which include preconcentration factor of 4.8 104.

Reference:
(1) Confocal Raman Microscopy for in Situ Detection of Solid-Phase Extraction of Pyrene into Single C18–Silica Particles. Link to the article

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