Simultaneous liquid phase microextraction with multiple solvents

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In a recent article published in Analytical Methods, researchers from the Shanxi Medical University at China have presented a novel microextraction approach for the determination of flavanoids and anthraquinones from traditional Chinese herbs. The authors use two different organic solvents placed in two filter membranes as extraction device. The main advantage of the so-called multiple-solvent simultaneous microextraction (MSSME) are the wide exchange surface and the selective extraction provided by the organic solvents used.

The miniaturized extraction unit (see Figure) was constructed as follows. Two square pieces (1cm X 1cm) of filter membrane were separately immersed in 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]) and decanol for 10 s. In this way, the pores of the membrane are impregnated with the extractants. The excess of the solvents was removed using absorbent paper. Once prepared, the solvent impregnated membranes were pierced by a microsyringe needle. The final configuration includes a rubber stopper which allows its coupling with the vial containing the standard solution or the sample. The extraction of flavanoids and anthraquinones is carried out within 40 min under continuous stirring. Before the elution, the two filter membranes are washed with double distilled water and then 50 µL of methanol was added to remove the analyte from the membrane. Aliquots of 20 µL were injected in the liquid chromatograph for the separation and UV detection of the analytes. To avoid carry over, a fresh MMSME unit was used for each extraction.
 
Figure. Scheme of the extraction device
All the variables affecting the extraction procedure were deeply studied, among with, the type of extractant was the most relevant. Indeed, three ionic liquids and six alkanol were studied.The final configuration provides enrichment factors between 68 and 132 with detection limits lower than 0.96 ng/mL with a precision better than 9 %.

The authors have included a critical evaluation of the proposed microextraction units as well as an analytical comparison of MSSME with other counterparts. We strongly recommend this article to our readers.

Reference:
(1) Novel multiple-solvent simultaneous microextraction for flavonoid and anthraquinone preconcentration in traditional Chinese medicine. Link to the article


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