Ultrasonic Soxhlet Extraction

• Ultrasonics improves the conventional Soxhlet extraction.
• The ultrasonically assisted Soxhlet extraction can lead to higher yields and shorter extraction times.
• The ultrasonic equipment can be easily combined with the classic Soxhlet extractor.

Soxhlet Extraction

Soxhlet extraction is a frequently used solid-liquid extraction method in the synthetic or analytical laboratory and is required when a desired compound shows only a limited solubility in a solvent, and the impurity is insoluble in that solvent. In brief, the working principle of the Soxhlet extraction can be described as a solvent-based reflux.
Ultrasound is successfully integrated into Soxhlet extraction to increase yield and to shorten the duration. When the Soxhlet extraction is completed, the solvent is removed (e.g. using a rotary evaporator).

Problem:

The traditional Soxhlet extraction has major disadvantages due to its long extraction duration and the large amount of solvent used. Furthermore, in a conventional Soxhlet extractor no agitation can be integrated to accelerate the extracting process. As large amounts of solvent are used, an highly energy consuming evaporation and concentration are required. Often, the thermo labile target compounds are decomposed as the material is exposed during the long extraction duration to the heat of the boiling point of the solvent.

Solution: Ultrasonic Soxhlet Extraction

Powerful ultrasound increases the mass transfer between sample and solvent. Thereby, solvent use can be reduced or completely avoided. The extraction duration is drastically shortened so that the extracts are not exposed to long heating period. This means that decomposition of the extract can be avoided.
Ultrasound can be easily integrated into a Soxhlet extraction setup – either by introducing the ultrasonic horn into the Soxhlet chamber or by sonication the Soxhlet chamber indirectly through the vessel wall. The ultrasonic Soxhlet extraction results in a higher yield within shorter extraction time under milder extraction conditions.

“Ultrasonication as an extraction method is an efficient technique when compared to reflux methods for extracting trace organics from soils and sediments. Ultrasonic extraction techniques proved to generate comparable or even greater quantities (Song et al., 2002) of hydrocarbons than other techniques of extraction […]. Depending on the type of contaminants and matrix, sonication can have the advantage of faster extraction times. Optimisation of the ultrasonic extraction parameters, including type of solvent or solvent composition, extraction time, sample load, and water content are required many times for more efficient and reproducible extractions (Berset et al., 1999). Ultrasonication techniques usually provide a relatively low cost method, using small volumes of organic solvent without the need of elaborate glassware and instrumentation.”
[Oluseyi et al. 2011]