Buffer solutions are very useful in a wide range of industrial processes. They are also vital to many biochemical systems.
Manufacture of shampoos
In the manufacture of shampoos, a citric acid/citrate buffer is added to the solution to maintain the pH of the shampoo at a slightly acidic level (about pH = 5.5).
Another important chemical found in most shampoos is sodium lauryl sulphate (SLS), a surfactant that breaks down oils and dirt. However, SLS can also affect the pH of the shampoo. When SLS comes into contact with water, it undergoes hydrolysis, producing hydroxide ions (OH−). These ions can increase the pH of the shampoo, making it more alkaline.
The impact of an increased pH becomes evident on the hair cuticle, the outermost layer of each hair strand. The cuticle acts as a protective barrier, preventing harmful chemicals from penetrating deeper into the hair. It is made up of overlapping layers of keratin, a tough fibrous protein composed of amino acids, each with a carboxyl group (-COOH). When the pH of the shampoo rises and hydroxide ions are present, these ions can deprotonate the carboxyl groups on the keratin, increasing the negative charge on the cuticle cells. As a result, the cuticle layers begin to repel each other and lift up.
This opening of the cuticle is undesirable because it allows damaging chemicals to enter the inner layers of the hair, potentially causing damage over time. Therefore, maintaining the right pH in shampoo is crucial for preserving the health of your hair.
Fermentation of alcoholic beverages
During fermentation of alcoholic beverages, yeast enzymes convert sugars to alcohols:
These enzymes function optimally within a certain pH range, usually 4 < pH < 7. If the solution is either too acidic or too alkaline, the enzymes are inhibited and/or yeast may not survive.
Carbon dioxide formed during fermentation acidifies the solution via the following equilibria:
Therefore, the change in pH during fermentation can be resisted by the addition of bicarbonate salts or using a phosphoric acid/phosphate buffer.
Biological buffers
Finally, human biological fluids require constant pH levels for biochemical processes to function properly.
The pH of blood (pH = 7.4) is maintained by a carbonic acid/bicarbonate buffer, while the pH of intracellular fluid is stabilised by the carbonic acid/bicarbonate buffer, protein buffers and the dihydrogen phosphate/hydrogen phosphate buffer.