Possibilities for Using Raman Spectroscopy to Determine the Amount of Analyte Directly from a Solid-Phase Extraction Cartridge in Water-Based Applications

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Abstract
Raman spectroscopy is occasionally used as a detection technique in liquid chromatography. This paper shows that the amount of analyte can also be determined directly from a solid-phase extraction cartridge, which eliminates the need for solvents in the analysis. Transmission geometry was used in Raman probing of the sorbent bed and interferences from the tube material were reduced by using quartz glass instead of the commonly used plastic. Bonded-phase silica C18 was a test sorbent, and ethylbenzene, as a test analyte, was extracted from its water solutions. A detection limit of 3 μg/mL was obtained in the Raman calibration by using a univariate method with a CH band of the sorbent ligand as an internal standard. This is only an order of magnitude higher than what was estimated for liquid chromatography with the same Raman instrument as its detector. In addition, an optimal sorbent for each analyte can be chosen more freely if there is no need to bother about further elution of the analyte.