Accelerated solvent extraction devices

As shown in Table 19.2, extraction with the mixture of methanol-water provides adequate extraction efficiency for most of the samples. However, this technique should be automated and the duration of sample preparation should be reduced. The usual methanolic extraction is carried out with the help of a shaking device and the total time of sample preparation including centrifugation and manual separation of the phases may be as long as 10-12 h. Recently, two new techniques have been introduced that can replace the traditional approach, that is, the accelerated solvent extraction (ASE), sometimes referred to as pressurized liquid extraction (PLE), and the MW assisted extraction (MAE). 

The accelerated solvent extraction (ASE) system introduced by Dionex uses standard solvents at elevated temperatures and pressures to increase extraction efficiency. Samples are placed in stainless-steel extraction vessels that are loaded into the ASE that has been programmed for the extraction protocol. The instrument allows for the unattended extraction of 24 samples. The initial units allowed for solvent blending by premixing solvents before they were placed into the ASE. Recent modifications allow solvent blending to be accomplished in-line. There has been some controversy about the use of the name ASE because it points to instrumentation from one company and other companies have introduced competing products. It has been proposed that the ASE technology be more correctly referred to as pressurized fluid extraction because ASE denotes a commercial device. 

More efficient devices are commercially available. One of these is the Accelerated Solvent Extractor sold by DIONEX, " where the extraction takes place in a closed vessel in which temperatures of 100°C and pressures up to 2000 psi are reached even with low boiling solvents. 

Figure 5 Manifold for dynamic MAE. 1, Solvent 2, pump 3, microwave oven 4, extraction chamber 5, temperature set-point controller 6, thermocouple 7, fluorescence detector 8, recording device 9, restrictor 10, extractor. (Reproduced with permission from Luque de Castro MD and Luque-Garcia JL (2002) Acceleration and Automation of Solid Sample Treatment, Elsevier.)...

---