The Gregar Extractor

The Gregar Extractor is a compact, simple-to-use yet versatile laboratory extractor developed by Master Glassblower Joe Gregar and Chemist Ken Anderson of Argonne National Laboratory. Its innovative design enables it to be used for a variety of different types of extractions, including:

• Solid-liquid extractions
• Liquid-liquid extractions with an immiscible solvent of higher density than the liquid being extracted
• Liquid-liquid extractions with an immiscible solvent of lower density than the liquid being extracted
• Because of its innovative design and ability to perform multiple type of extractions (which in the past would have required multiple separate extractors), the Gregar Extractor was awarded an R&D 100 award in 1999.

The basic components of the extractor are illustrated below. It consists of a body, a primary condenser, a receiving flask, and depending on the type of extraction to be performed, either a thimble or a solvent guide. An auxiliary or secondary condenser can also be used if desired.

(Note, exact configuration and proportions may vary from those illustrated.)

The Gregar Extractor operates on the principle of continuous displacement. Solvent is distilled from the receiving flask into the extractor body via the vapor arm and condensed at the condenser. From the condenser, the solvent drips into the body where it comes in to contact with the material (solid or liquid) to be extracted. As fresh solvent is condensed into the body, solvent which has already been in contact with the substrate is displaced out of the body and returned to the receiving flask.

The extractor can easily be configured to perform several different types of extraction by varying the position of the two three-way valves . This flexibility is the basis for the Gregar extractor's versatility. However, it is possible to mis-configure these valves, which can result in inefficient or no extraction. Proper configuration for solid-liquid, and both types of liquid-liquid extraction are illustrated and discussed below.

Solid-Liquid Extractions

When used for solid liquid extractions, the Gregar Extractor is configured as illustrated at left. The lower valve is aligned such that solvent flows out of the bottom of the body and into the solvent return arm. Solvent flow from the body or solvent return arm directly into the receiving flask is prevented. The upper valve is configured such that solvent flows up the solvent return arm to the level of the valve then overflows into the vapor arm and from there is returned to the receiving flask by gravity.

The solid to be extracted is loaded into the extraction thimble, which is placed inside the extractor body. Depending on the nature of the sample, the material may either be placed directly into the glass thimble, or, in the case of fine powders or other samples which might clog the glass frit at the bottom of the extraction thimble, into a cellulose, glass fiber or other fine porous thimble which is then placed inside the glass extraction thimble.

As solvent is distilled into the body from the receiving flask, the natural tendency of a liquid to find its own level causes the solvent to rise in the solvent return arm. When this level reaches the level of the upper valve, the solvent is able to "spill" over into the vapor arm and, hence, return to the receiving flask. As more solvent is continuously distilled into the body and is condensed at the condenser, solvent already present in the body (i.e that has already been in contact with the solid to be extracted) is continuously displaced out of the bottom of the extractor body, carrying with it extracted soluble products, and is returned to the receiving flask. This continuous cycle effectively extracts the sample by maintaining a continuous slow flow of solvent over the sample. Because the solvent level is constant, and the sample fully immersed in solvent at all times, sample packing, solvent channelling and other problems which can plague conventional solid liquid extractors are eliminated.

Liquid-Liquid Extractions 1:  Extracting with an immiscible solvent of higher density than the liquid being extracted.

When using the Gregar Extractor for liquid-liquid extraction in which the extraction solvent is of higher density than the liquid being extracted, the extractor is configured in the same way as for solid liquid extraction. That is, the lower valve is aligned such that solvent flows out of the bottom of the body and into the solvent return arm. Solvent flow from the body or solvent return arm directly into the receiving flask is prevented. The upper valve is configured such that solvent flows up the solvent return arm to the level of the valve then overflows into the vapor arm and from there is returned to the receiving flask by gravity. the principle difference between these extractions and solid liquid extractions is that a glass thimble is not required.

In this type of extraction, the solvent is distilled from the receiving flask to the body via the vapor arm, condensed at the condenser and allowed to drip into the liquid to be extracted. Contact between the solvent and the immiscible liquid to be extracted is achieved by the drip action, but can be enhanced in a variety of ways (use of glass beads, for example) if necessary. Because of its higher density, the extraction solvent sinks through the liquid being extracted and accumulates at the bottom of the extractor. As in the case of solid liquid extractions (above) as solvent accumulates in the body of the extractor, gravity forces solvent out of the bottom of the extractor and into the solvent return arm, and hence, back to the receiving flask via the vapor arm.

Liquid-Liquid Extractions 2:  Extracting with an immiscible solvent of lower density than the liquid being extracted

For this type of extraction, the Gregar Extractor is configured differently than for Solid-Liquid or Liquid-Liquid extractions is which the extraction solvent is of higher density than the liquid being extracted. In this case, the upper valve is configured so that solvent is able to flow out of the extractor body and into the solvent return arm. The lower valve is configures such that solvent in the solvent return arm is drained into the receiving flask. Unlike the above cases, flow out of the bottom of the extractor is prevented. Also, in this case a solvent guide is added to force solvent to contact with the liquid being extracted.

In this type of extraction, Solvent is distilled from the receiving flask into the body of the extractor and condensed at the condensor. From the condensor, the solvent drips into the solvent guide, which is placed into the liquid being extracted. As solvent accumulates in the guide, the weight of solvent will displace liquid out of the solvent giude. When all of the liquid in the solvent guide has been displaced by solvent, condensation and accumulation of additional solvent will force solvent out of the bottom of the solvent guide. Due to its lower density, the solvent will then float up through the liquid being extracted and accumulate as a layer at the top of the liquid. When sufficient solvent has accumulated so that the level in the body reaches the level of the solvent return arm, solvent will spill over through the solvent return arm and returned to the receiving flask.