What is the Effect of Temperature and pH on Extraction?

Extraction is simply the collection of important active substances from the raw material or drug material in pharmaceutics. This can be done either physically or by dissolving a liquid solvent like water and alcohol, generally termed menstruum. The effect of temperature and pH controls the extraction. This process is discussed below.

History

Medicines have been obtained from plants or their products, which were steeped in or boiled in various liquids. Solvents, alcohols and vinegar made the ingredients’ extraction more efficient and also provided the benefit of preservation. Plants were prepared and kept in the best state for ease of extraction and better products. The required part was cut into small fragments, dried and then powdered. From the 1800s, the production of medicines on a large scale led to the industrialisation of the extraction process by machinery in big factories.

Extraction

Types of extractions

• Dry extract like tablets and capsules in the case of belladonna extract.
• Soft extract like ointment and suppository in case of glycyrrhiza extract.
• Liquid extract, as in the case of a tincture.

Ideal Solvent

An ideal solvent should be highly selective for the compound which has to be extracted and should not react with the extracted substance as it can then alter the chemical required. However, it should be cheap, eco-friendly, and aptly dense. Its density should vary with the density of water having a minimum viscosity.

Methods of Etraction 

• Infusion:  Infusions are freshly prepared by macerating the crude drug in a short period by cold or boiling it in water. The product is a dilute solution.
• Decoction: The crude drug is boiled for a defined time in a specified volume of water, and when it is cooled, it is filtered.
• Maceration: In a stoppered container, solid ingredients are placed for 3-7 days in a whole solvent and then frequently agitated. This mixture is now strained and then clarified.
• Percolation: The solvent is continuously displaced downward through the crude drug bed, usually for tinctures and fluid extract.
• Distillation: This method is based on the principle of different boiling points of other substances for separation. It is more of a physical process than a chemical.
• Centrifugation: It works on the principle of the effect of gravity on the particles. In this process, the substances are separated and suspended in a liquid medium.
• Chromatography: This is one of the most important separation and extraction techniques. The mixture distributes itself between stationary and a mobile medium.

Effect of Temperature on Extraction

The main controlling factor remains the temperature in the extraction, be it any method of doing so. All the processes require a certain temperature at which the extraction process can begin; this temperature is known as an optimal temperature. Some processes may directly depend on heat like distillation, decoction and others, but some are indirectly dependent on the room temperature, as in the case of chromatography, maceration and infusion. It has been noted that for every increase in temperature, the extraction process speeds up. Extraction is directly dependent on temperature but up to a limit. After reaching the point of saturation, there is no effect of temperature on extraction. 

In some cases, there is a decrease in extraction with every temperature rise. This depends on the nature of the substance extracted from the drug material and sometimes the solvent. However, the effect of temperature on extraction in pharmaceutics remains the most crucial point. Other factors like the pressure, nature of solvent and nature of drug material may also contribute to the extraction process.

Effect of pH on Extraction

Other than the temperature, the governing factor of extraction is the pH of the solvent and the drug material. Different types of drugs depend on different pH.pH may be acidic, basic and neutral, but there is a specific pH for every extraction in the extraction of pharmaceutics. Only acidic and basic pH may not work. There is a range of pH in which the extraction is possible, but the extraction is best at optimal pH. 

Summary

This article explained the extraction, its methods and the factors governing the process of extraction in pharmaceutics. Here we briefly discussed the effect of temperature and pH on extraction. There are many types of extractions used in the industries, and all of them use different methods which work on different principles based on the drug which has to be extracted. It is essential to select the correct solvent for our extraction because the wrong solvent may prove to be a disaster, and the extraction process would have no meaning to it. Similarly, the best way to extract an active substance from the drug material is to do the extraction at optimal temperature and optimal pH though sometimes a temperature rise may help speed up the process.