In-line cold column trapping of organic phase in dispersive liquid–liquid microextraction

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Dispersive liquid-liquid microextraction (DLLME) was firstly proposed by Rezaee et al. in 2006 (1) as a simple, rapid and cheap extraction technique capable to provide high recoveries and enrichment factors. In DLLME, the organic acceptor phase is dispersed into the sample assisted by an appropriate solvent or by an external energy source (like ultrasounds) producing a cloudy solution. As a consequence of the dispersion, the surface to volume ratio of the acceptor phase increases dramatically, making easier the mass transference through the interfase and therefore reducing the extraction times and increasing the enrichment factors. After the dispersion, the organic extractant should be recovered for its final analysis. This final step is the limiting factor of the technique since in most of the cases a centrifugation step is required. Despite its efficiency, the centrifugation step is an off-line process which avoids the potential automation of the technique and therefore its integration with commercial instruments.

Different approaches have been proposed in the last years to avoid the centrifugation step. On the one hand, Cruz-Vera and co-workers proposed in 2009 an in-syringe method which simplifies the phase´s separation process (2) while Maya et al. used a similar process for the direct combination of DLLME with HPLC (3). On the other hand, Anthemidis et al. proposed a microcolumn filled with PTFE-turnings as trap for the organic solvent which is adsorbed and efficiently separated from the sample matrix (4).


In a recent article accepted for publication in the Journal of Chromatography A, researchers from the University of Lorestan at Iran have proposed an in-line cold column trapping to recover the organic phase after its dispersion. The core of the system consists of a column filled with silica particles located in a cooler which can operate in the range from -10 to 80 ºC with an accuracy of 0.1ºC. This approach takes also advantage of the high melting point of 1-dodecanol (24 ºC) which is employed as extractant phase. In the general procedure, the cloudy solution obtained after the extractant dispersion is transferred to the column which is fixed at a temperature of 10 ºC. At this temperature, the solvent solidifies being retained in the column. Once the solvent has been separated from the sample matrix, the temperature of the column is increased up to 35 ºC and 500 µL of ethanol are used to recover the 1-dodecanol with the extracted analytes.

The new approach has been applied for the extraction of curcumin form human serum with excellent recoveries and precision values. In the article, the readers will find the deep description of the proposed manifold as well as its optimization and analytical characterization.  Moreover, we recommend the article of Leong and Huang where DLLME based on solidification of floating organic drop is proposed for the first time (6).

References:
(1) Determination of organic compounds in water using dispersive liquid liquid microextraction. Link
(2) One step in-syringe ionic liquid-based dispersive liquid liquid microextraction. Link
(3) Completely automated in-syringe dispersive liquid liquid microextraction using solvents lighter than water. Link
(4) On-line sequential injection dispersive liquid–liquid microextraction system for flame atomic absorption spectrometric determination of copper and lead in water samples. Link
(5) In-line cold column trapping of organic phase in dispersive liquid–liquid microextraction: Enrichment and determination of curcumin in human serum. Link
(6) Dispersive liquid–liquid microextraction method based on solidification of floating organic drop combined with gas chromatography with electron-capture or mass spectrometry detection. Link

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