Extraction microscale

Discontinuous methods are performed in conventional separating funnels in one or more steps. In ultratrace analyses, tapered or specially profiled quartz tubes are recommended because of their easier cleaning (more compact size), the introduction of less contaminating material, and easier centrifugation in the case of difficulties with phase separation. Shaking must be continued until equilibrium is reached, which may last seconds, minutes, or (rarely) hours, depending on the physicochemical properties of the system more than 2-5 min requires a mechanical shaker. Microscale extraction carried out in autosampler tubes, followed by direct automatic introduction of the organic phase into the atomizer, is recommended. 

In a student experiment designed to demonstrate microscale extraction techniques, the three compounds shown in Figure 1 arc dissolved in diethyl ether and separated. Their physical properties are shown in Table 1. 

An extractor that operates on the same principle, but for microscale extractions, is shown in Figure 10-5, p. 110. 

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. 

A microscale extraction process consists of two parts (1) mixing the two immiscible solutions, and (2) separating the two layers after the mixing process. 

A major difference between macro and micro techniques is that when microscale volumes are used, as just discussed, the mixing and separation are done in two parts. When macroscale volumes are used in a separatory funnel, mixing and separation are both done in the funnel in one step. The separatory funnel is an effective device for extractions with larger volumes, but it is not practical for microscale extractions because of the large surface areas involved. 

Microscale extractions of trimyristin from nutmeg, and cholesterol from gallstones, have been described. Diethyl ether was used as the solvent in both cases. A packed Fhsteur pipet column was used for filtering, drying (nutmeg experiment), and decolorizing (gallstone experiment). 

C, pressure 350bar, time 6h, flow rate 20kg CO2 per h for the extraction of usnic acid from Usnea barbata. For microscale extraction, acetone is recommended, as most lichen substances are soluble in this solvent. The use of the microextractor shown in the monograph of Asahina and Shibata (1954) cannot be recommended because of the risk of inflammation of the solvent. A simple and safe device is shown in Fig. 4. 

To extract solid substances with hot organic solvents, a commercial Soxhlet extractor is fully sufficient. For microscale extraction the apparatus according to Blount (Fig. 8) can be used. Microscale extraction with high-boiling solvents is carried out in a Haanen and Badum extractor (Fig. 9). Among the apparatus for perforation, two types need to be considered ... 

The small injection volume of CE is desirable only when a small amount of sample is available. With materials which are heterogeneous on a microscale the need for extraction/dissolution of representative... 

Smith, M., G. E. Collins, and J. Wang. Microscale solid-phase extraction system for explosives. J. Chromatogr., A 991, 159-167 (2003). 

Two types of SFE equipment are used. One is a large scale flow type apparatus(1.5Q which is used to obtain the total extracts. The SFE condition in this equipment was 50 °C and 30 MPa. The other is a microscale extractor(60 ml) which is used to establish the optimal SFE conditions. In the SFE, carbon dioxide is mainly used and the experiment is performed in the ranges of 35-55 °C and 10-30 MPa. 

DNA extraction and purification were traditionally accomplished using organic extraction and ultracentrifugation-based procedures, which are both time-consuming and not easily transferable to the microscale. Newer methods employ solid-phase extraction (SPE) on silica surfaces, glass fibers, modified magnetic beads, and ion-exchange resins—techniques that save time and are also more amenable to chip applications. 

Neame, K. D., and Richards, T. G. (1972). Elementary kinetics of membrane transport. BlackweU. Nguyen, R. T., and Harvey, H. R. (1994). A rapid microscale method for the extraction and analysis of protein in marine samples. Mar. Chem. 45, 1-14. 

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