Extraction

The products above all represent the solid-liquid extraction technique. 

In the most common applications in our industry, a combination of a solvent and organic material creates a new mixture that can then be distilled or purified to create a final product.

Pictured above is an expanded view of our Benchtop Filtration Funnel, which lets you to separate solids from liquids. Not pictured is the filter paper that lines the inside, which is also an essential component of this technique.

Because the solvent itself is undesirable in a commercial product, you should normally perform some kind of solvent recovery to purify your final product and reclaim valuable solvents for later use.

For the more technical amongst you, here is a handy guide to some of the most common extraction techniques employed in laboratories today.

Common types of extraction:

Solventless Extraction

Solventless extraction can be described as any process which does not use a solvent to obtain an extract. Even relatively straightforward extraction via heat and pressure can technically be considered a solventless procedure.

One of the most common methods used today is to combine heat and pressure to squeeze products out of crude samples. The resultant products are “purified” to an extent by this simple process. Without much effort, you can force constituents out of your sample, based largely on the pressure and temperature applied.

An example of this technique in action would be a rosin press or a hydraulic press.

Extraction Using Solvents

Another commonly-used method involves combining a liquid or solvent (such as water or alcohol) with an insoluble product. The product becomes suspended in the liquid, but it never dissolves. This property is important, because the non-dissolved product may then be filtered out by a series of finer and finer woven meshes, to collect different grade products depending on the size of filter used.

Solvents can remove (or extract) compounds based on their polarity. Molecules are either polar or non-polar, and they can be extracted out of a mixture of compounds by closely matching the solvent’s polarity to the polarity of the molecule you wish to extract.

This method works well for extracting products, but you may also end up with other, closely-related molecules.

Below are some more common extraction methods:

Liquid-Liquid Extraction

Separating compounds via liquid-liquid extraction is based off the different solubilities of two liquids that do not mix, such as a polar and non-polar liquids.

A common example would be water and a non-polar solvent. This extraction process allows molecules to cross the barrier between the two liquids, and it is usually carried out in a separatory funnel when performed on a small scale.

Solvents that have a higher solubility (and closer polarity) will have the product extracted into them during the liquid-liquid extraction process. The two immiscible liquids may then be separated, and the desired product concentrated.

Supercritical

This method of extraction pressurizes a solvent into a supercritical state. When enough pressure and temperature is applied to a solvent, it will become supercritical (if it surpasses the molecule’s critical point).

When this happens, the barrier between liquid and gas are eliminated, and they can be fine-tuned to act like a gas, liquid, or an in-between state of both.

Supercritical fluids have both properties, so the ability to tune them precisely is extremely valuable.

This procedure allows for greater control over which products will be dissolved in the solvent.

Solid-phase

Solid phase extraction is a method that has both a mobile and a stationary phase. These two phases work in conjunction to extract the compounds you’re looking for. The stationary phase and mobile phase will vary drastically depending on the results you are trying to achieve.

A mobile phase can either be pulled, pushed, or gravity-fed through the stationary phase. The mobile phase now moves through the stationary phase and can separate the constituents in the mobile phase.

Stationary phases can retain molecules from the mobile phase via polarity, size exclusion, and ionic interactions, depending on the phases chosen. An example of such extraction is High Performance Liquid Chromatography.

Final remarks:

We’ve only just scratched the surface of how extraction works in the laboratory. Stay tuned on our blog page, where we’ll post more guides and practical tips for getting the most from extraction in your own set-up.