Solid-liquid extraction, automatic

Gonzales, M., Gallego, M., and Valcarcel, M., Liquid chromatographic determination of natural and synthetic colorants in lyophilized foods using an automatic solid-phase extraction system, J. Agric. Food Chem., 51, 2121, 2003. 

Figure 4.23 Illustrates another alternative for the separation of both phases once the batch liquid-liquid extraction has been finished. Formerly conceived for solid-liquid extractions, this complex mechanical assembly [20] consists of two automatic burettes for addition of the two phases, the extractor —moveable in various fashions— and a vertically moving paddie stirrer. The extraction vessel rotates at a high speed, which promotes phase separation, as shown in the figure. The lighter phase creeps up the walls and passes to an upper receptacle —the separation is facilitated by adding more aqueous phase. Once separation Is complete, an aspiration probe withdraws the organic phase. Finally, a mechanical system turns the vessel over for cleaning.

The automation of the use of disposable cartridges for solid-liquid extraction connected directly with a liquid chromatograph poses major techical problems which are, however, lessened by robotics. Although several partly automatic systems have been described [23-26], there is only one really completely automated system, which was reported recently [27]. It is an automated cartridge exchange module combined with a low-cost purge pump, a solvent selec-... 

If a solid substance is extracted repeatedly with several portions of cold solvent, the operation is called maceration, if the same operation is carried out with hot solvent, it is called digestion and if the procedure has a countercurrent character, it is called percolation. So-called Soxhlet extractors, in which a solid substance is extracted with a solvent and the extract becomes more and more concentrated, function automatically. If a dissolved substance is extracted with one portion or more of an immiscible solvent, the operations is called simple extraction or multiple extraction, respectively. If the extraction is carried out by countercurrently-moving solvents, we deal with a countercurrent distribution technique. A continuous extraction of a liquid with another liquid immiscible with the first is called perforation continuous countercurrent extraction using two liquid phases is carried out in special countercurrent columns. If one of the phases is fixed on a carrier, partition chromatography is the name given to the operation. The choice of the given type of extraction method will depend on the character of the analyzed substances and on the required separation efficiency. 

Oliveira HM et al (2010) Exploiting automatic on-line renewable molecularly imprinted solid-phase extraction in lab-on-valve format as front end to liquid chromatography application to the determination of riboflavin in foodstuffs. Anal Bioanal Chem 397(1 ) 77-86... 

The operating conditions for solid-state fermentation for cellulase production are dependent on the strain to be used, the reactor type and the medium composition, but the basic operating procedure remains the same as shown in Fig. 2. The final product can be obtained as crude solid cellulase, liquid cellulase or powder cellulase according to the application. Figure 3 shows a process flowsheet for cellulase production [25]. In the process, wheat bran is used as substrate. Seeds are prepared in a stirred-tank fermentor and then sprayed into the medium by a spray distributor. The fermentation is performed in a shallow-tray fermentor. The temperature and humidity in the fermentor are automatically regulated. After fermentation, cellulase is recovered by water extraction and purified by salt precipitation and ion exchange. The final product is concentrat-... 

In the following examples, HP7680 SFE instruments (Hewlett-Packard) were used. With these instruments, samples are input to the instrument via containers referred to as extraction thimbles. Extracted components are collected and concentrated on soUd traps. The temperature of the solid trap can be independently set for extraction and reconstitution steps in a method. The chemical functionahty (none to quite polar) of the trap is selected by the choice of the packing material. A reconstitution solvent is used to move extracted components from the solid trap to automatic liquid sampler vials (or to waste). Depending upon the appUcation, the vials are presented to a subsequent analytical instrument or possibly manipulated for a gravimetric assay. With this instrument implementation, samples are input and fractions of extracted components in hquid solvents in 2-mL vials are output with no manual intervention between input and output steps. 

Solid phase extraction has several advantages over conventional liquid-liquid extraction when trace components are of interest. It is faster, requires less solvent, reduces the need for large concentration steps, and is easily automatable. Several liters, if necessary, can be poured through the column, and the trace components collected. These can be eluted with only a few mL of solvent, so the solvent removal for further concentration is nearly or completely eliminated. However, an HPLC column of 30 cm can provide 15,000 plates, whereas a solid phase disc can provide only 10 to 50 plates. What this means is that a solid phase disc can separate classes of compounds, but HPLC can then separate the compounds within that class. In fact, one of the major uses for SPE is as a clean-up for HPLC. The sequence is (1) select the proper size SPE tube, (2) condition the tube, (3) add the sample, (4) wash the packing, and (5) elute the compounds of interest. 

In order to apply an analytical method it is compulsory to avoid interferences between the analyte and the components of the matrix. Therefore, most of the time, the analysis begins with the separation of the components from the sample matrix. The gaseous pollutants, trapped in solid or liquid matrix will be extracted using the methods described in this chapter. The results of the analysis depend on the preparation step. The influence oft his step is comparable with the precision of the analytical devices. So, designing the preparation method received all the attention and uses all the recent developments in chemistry and automatics. 

SPE solid-phase extraction LLE liquid—liquid extraction GPC gel permeation chromatography ATD automatic thermal desorption... 

This selective lixiviation or dissolution operation can be performed automatically by the Technicon SOLIDprep II module. The undissolved solid gathers in the bottom of the extraction vessel, so that the aspirating pipette readily withdraws the supernatant liquid. 

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