Bell-shaped extraction, a new liquid-liquid microextraction format

Single drop microextraction (SDME) can be considered the first technique in the liquid phase microextraction context. It is a simple procedure which involves sampling and injection in the same device in a similar way to solid phase microextraction. In this case, a small drop (usually in the range from 1 to 5 µL) is suspended in the needle of a microsyringe which is immersed in the sample or kept into close contact with its headspace. Single drop-based microextractions usually present problems derived from the instability of the drop which results in its detachment when volumes higher than 5 µL are employed. This limitation has also a clear influence in the absolute recovery of the extraction technique and it may restrict its coupling with liquid chromatography where higher injection volumes are required.

In 2006, Lu et al. presented the so-called directly suspended droplet microextraction (DSDME) which overcame some of these limitations. This single drop-based technique consists in the location of a small drop of solvent (10-50 µL) in the vortex of a stirred solution or sample. The general procedure (described in Figure 1) involves four well defined steps, namely: (a) stirring of the solution; (b) location of an organic solvent lighter than water in the vortex; (c) extraction of the target analytes, and (d) recovery of the organic drop for its subsequent analysis.

Figure 1. General procedure of directly suspended droplet microextraction

The recovery of the solvent after the extraction requires special skills in order to recuperate all the extract without any trace of the sample matrix. In a recent article published in the Journal of Chromatography A, Cabala & Bursova present a bell-shape device which acts as receptor of the organic phase before and after the extraction. In this sense, the authors describe a modified procedure which is schematically presented in Figure 2. It consists on various and subsequent steps, involving: (a) introduction of the bell-shaped receptor in the extraction vial; (b) introduction of the organic phase with a syringe; (c) stirring of the solution in order to form a vortex where the extraction phase is located; (d) extraction of the analytes; and (e) final  recovery of the extractant.

Figure 2. General procedure of directly suspended droplet microextraction

According to the results, the new proposal is a useful extraction procedure which provides high enrichment factors with good precision values. For more detailed information (e.g optimization of the bell receptor or selection of the organic solvent) readers are referred to the original article.

References:

Link to article: Bell-shaped extraction device assisted liquid–liquid microextraction technique and its optimization using response-surface methodology

Link to article:Directly suspended droplet microextraction