Accelerated Solvent Extraction (ASE) is an innovative extraction technique that reduces extraction times and consumes less solvent compared to more traditional extraction techniques such as soxhlet or sonication. ASE significantly reduces extraction times — increasing the sample extraction kinetics by performing solid–liquid extractions at temperatures above the solvent's boiling points. ASE uses high pressure to keep the solvent liquid at these higher temperatures and to also increase the matrix penetration by the solvent. The combination of high temperature and pressure enables the ASE extractor to perform fast extractions with minimal solvent use while ensuring excellent analyte recoveries.
Not uncommon in the extraction process of any technique is the need for additional clean-up steps on the extract prior to analysis. ASE will produce a clean extract with most samples, and the cleanliness of the extract is dependant on the sample matrix. Matrices that are more complex can sometimes produce extracts with unwanted co-extractables. In the past this was solved by filtering the extract through different sorbent materials to remove the unwanted compounds. While this technique worked well, it added an extra step or two to the process as well as the possibility for technician error during the transfer. Recent studies on several different matrices have shown that these post extraction clean-up steps can be eliminated by adding various sorbent materials directly to the ASE extraction cell. The extraction and clean-up are performed within the extraction cell, producing a clean extract that is ready for analysis.
Table 1: Recovery data for ASE extraction of perchlorate.
Figure 1 shows an example of placement of sorbents in the ASE extraction cell. When extracting perchlorate from various food samples, for example, adding a mixture of ion-exchange resins to the extraction cell removes interfering anions and adding basic alumina removes colour. The collected extracts were then ready for ion chromatography. Table 1 shows the recovery data for ASE extraction of perchlorate from various samples with excellent recoveries. The samples were mixed with ASE Prep DE at a 2:1 ratio and this mixture was placed on top of the sorbent layers in the extraction cell. The samples were extracted with deionized water at 80 °C using three 5 min cycles.
Another example of in-cell clean-up involves using alumina in the extraction cell when extracting fish samples for PCBs. The alumina retains the lipids while allowing the PCBs to be extracted into the collection vial. Table 2 lists the recovery data for ASE extraction of fish tissue for PCBs. The samples were mixed with ASE Prep DE at a 3:1 ratio and this mixture was placed on top of the alumina in the extraction cell. The samples were extracted with hexane at 100 °C using two 5 min cycles.
Table 2: Recovery data for ASE extraction of PCBs from fish tissue.
1. "Dionex Application Note 322: Selective Extraction of PCBs from Fish Tissue Using Accelerated Solvent Extraction (ASE)," Dionex Corporation (Sunnyvale, California).
2. A. Muller, E. Bjorklund and C. von Holst, J. Chromatogr. A., 925, 197–205 (2001).
3. S. Sporring and E. Bjorklund. J. Chromatogr. A., 1040, 155–161 (2004).
4. M. Nording et al., Anal. Bioanal. Chem., 381, 1472–1475 (2005).
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