Single Drop Extraction

Single drop extraction (SDE) or liquid-phase microextraction (LPME) is a recently developed microscale extraction method. In this method a single liquid drop is used as a collection phase. Small volumes of organic solvent (from 0.5 pi to 2.5 pi) are used. The collection phase must have a sufficiently high surface tension to form a drop which can be exposed to the analyte solution. When the extraction is finished, the single drop is injected into the GC. A scheme of such a device is shown in Eigure 2.8. 

SDE can be used in static and dynamic modes. When working in the static mode, steps in the extraction process are (a) the magnetic stirrer is switched on to agitate the aqueous sample solution  

SDE avoids the problems of solvent evaporation as in LEE. It is a fast, inexpensive, and simple method. However, the extraction is not exhaustive. 

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Henschke M, Pfennig A. Mass transfer enhancement in single-drop extraction experiments. AIChE J 1999 45 2079-2086. 

Single-drop extraction of different types of analytes from liquid and gaseous matrices... 

M. Henschke and A. Pfennig, Mass Transfer Enhancement in Single-Drop Extraction Experiments. AIChE J., 1999, 45 (10), 2079-2086. 

Buszewski, B., Ligor, T. Single-drop extraction versus solid-phase microextraction for the analysis of VOCs in water. LC-GC Europe 2, 2-6 (2002)... 

FIGURE 2.8 Schematic of a single-drop extraction apparatus. (Reprinted from Buszewski, B. and Ligor, T., LC-GC Europe, 15, 92-97, 2002. With permission from Advanstar Communications.)... 

Interfacial Contact Area and Approach to Equilibrium. Experimental extraction cells such as the original Lewis stirred cell (52) are often operated with a flat Hquid—Hquid interface the area of which can easily be measured. In the single-drop apparatus, a regular sequence of drops of known diameter is released through the continuous phase (42). These units are useful for the direct calculation of the mass flux N and hence the mass-transfer coefficient for a given system. 

In the past decade, several novel solvent-based microextraction techniques have been developed and applied to environmental and biological analysis. Notable approaches are single-drop microextraction,147 small volume extraction in levitated drops,148 flow injection extraction,149 150 and microporous membrane- or supported liquid membrane-based two- or three-phase microextraction.125 151-153 The two- and three-phase microextraction techniques utilizing supported liquid membranes deposited in the pores of hollow fiber membranes are the most explored for analytes of wide ranging polarities in biomatrices. This discussion will be limited to these protocols. 

So far, LSE is the most popular for extracting contaminants in food. However, over the last years LPME in its different application modes (single drop microextraction, dispersive liquid-liquid microextraction and hollow fiber-LPME) has been increasingly applied to food analysis because of its simplicity, effectiveness, rapidity, and low consumption of organic solvents. Different applications have been recently reviewed by Asensio-Ramos et al. [112]... 

To enhance extraction efficiency in the SME system (also called single-drop microextraction [SDME]), He and Lee developed a procedure termed liquid-phase microextraction (LPME),89 which, in its static mode, resembles the SME system. 

Jeannot, M.A. and F.F. Cantwell. 1997. Mass transfer characteristics of solvent extraction into a single drop at the tip of a syringe needle. Anal. Chem. 69 235-239. 

Solvent Liquid/liquid extraction (LLE) Steam distillation/extraction (SDE) Solvent microextraction (SME) - SDME - LPME - DLLME Headspace-solvent-microextraction (HS-SME) - Headspace single-drop microextraction (HS-SDME) - Headspace liquid phase microextraction (HS-LPME) ... 

HSPE Headspace solvent microextraction HS extraction of volatile compounds into a single drop of solvent, which is then injected into the GC For volatile, GC-amenable compounds, particularly in water and flavor analysis... 

Lopez-Bianco, M.C., S. Blanco-Cid, B. Cancho-Grande, and J. Simal-Gandara. 2003. Application of single-drop microextraction and comparison with solid-phase microextraction and solid-phase extraction for the determination of a- and [1-endosulfan in water samples by gas chromatography-electron-capture detection. J. Chromatogr. A 984 245-252. 

Jermak, S., B. Pranaityte, and A. Padarauskas. 2007. Ligand displacement, headspace single-drop micro-extraction, and capillary electrophoresis for the determination of weak acid dissociable cyanide. J. Chromatogr. A 1148 123-127. 

There are many classical methods to investigate the chemical reaction and kinetics at the liquid-liquid interface, which include a Lewis cell, a single drop method, and rotating disc method [22]. All of these methods however could not measure both the extraction rate and interfacial concentration of extractant, simultaneously. Modern experimental methods of interfacial reaction can determine the interfacial species, interfacial concentration, and interfacial chirality of an extractant or complex as a function of time. 

Saraji and Mousavinia (2006) developed an efficient in-syringe derivatization step for fiaiit juices and fruits. The parameters for insyringe derivatization optimized with phenolic standards were found to be 10 min at room temperature with 0.7 pL A,0-Z A(trimethylsilyl) acetamide (BSA). Before derivatization, the samples underwent single-drop microextraction, where small volumes of organic solvents were used to extract analytes. The advantage of this approach is that it creates reduced risks for sample loss and contamination. 

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