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Soxhlet and Ultrasonic Extraction of Organics in Solids

Environment: Water and Waste

  1. G.R. Barrie Webster

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a0864

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Webster, G. B. 2006. Soxhlet and Ultrasonic Extraction of Organics in Solids. Encyclopedia of Analytical Chemistry. .

Author Information

  1. Websar Laboratories, Inc., MB, Canada

Publication History

  1. Published Online: 15 SEP 2006

Abstract

Soxhlet extraction is the removal and recovery of organic analytes from a permeable solid matrix by means of a solvent which is continually evaporated from a still-pot and condensed in such a manner that it falls into and permeates through the matrix which itself is held in a permeable container in a siphonable chamber. Soxhlet extraction has been used for over 120 years (since 1879) and is commonly used as a benchmark for total extractable organic residues.

Ultrasonic extraction is the removal and recovery of organic analytes from a permeable solid matrix by means of a solvent which is energized by sound energy at frequencies in excess of those audible to the human ear. Energy may be introduced into the sample by means of an ultrasonic probe which is inserted into the sample or an ultrasonic bath into which the sample plus solvent is immersed. The ultrasonic energy may be strong enough to disrupt and pulverize the matrix, thus increasing the extractability of the analyte.

The operation of the Soxhlet extractor is intuitively easy to grasp. Extraction is viewed as being complete or close to complete.

Ultrasonic extraction is convenient and straightforward. Ultrasonic baths provide relatively reliable sources of extraction energy.

Soxhlet extraction is solvent intensive and requires laboratory facilities in which flammable and toxic solvents can be used safely. The glassware required is expensive and vulnerable to breakage. Cooling of the condenser of the Soxhlet apparatus requires a constant supply of cooling water. Residues are concentrated in the still-pot and are thus vulnerable to thermal degradation. Only total residue can be extracted by Soxhlet extraction; little or no speciation is possible.

Ultrasonic extraction must be performed under conditions which protect the hearing of laboratory personnel. The ultrasonic generator may generate heat which may affect the extraction process. Ultrasonic probes become pitted when used for the extraction of abrasive matrices such as soil, thus changing the energy generated and affecting the extraction efficiency of the procedure. Ultrasonic baths provide less intense extraction energy. Extraction of total residue is the aim of ultrasonic extraction; little or no speciation is possible.