Sodium hydroxide is the principal strong base used in the chemical industry. In bulk it is most often handled as an aqueous solution, since solutions are cheaper and easier to handle. Sodium hydroxide is also used for the manufacture of sodium salts and detergents, for pH regulation, and for organic synthesis.
Sodium hydroxide is employed to digest tissues, such as in a process that was used with farm animals at one time. This process involved placing a carcass into a sealed chamber, then adding a mixture of sodium hydroxide and water. This eventually turns the body into a liquid with coffee-like appearance and the only solid that remains are bone hulls, which could be crushed between one's fingertips.
Surfactants can be added to the sodium hydroxide solution in order to stabilize dissolved substances and thus prevent redeposition. A sodium hydroxide soak solution is used as a powerful degreaser on stainless steel and glass bakeware. It is also a common ingredient in oven cleaners.
Sodium hydroxide is widely accepted for cleaning, sanitizing, and storing chromatography media and systems. The advantages of sodium hydroxide as a cleaning and sanitation agent are
- Efficacy
- Low cost
- Ease of detection
- Removal
- Disposal
Sodium hydroxide has been shown to be effective in removing proteins and nucleic acids. It is also effective for inactivating
- Viruses
- Bacteria
- Yeasts
- Fungi
- Endotoxins
It is common practice in industrial manufacturing to save time by adding a salt, such as sodium chloride, to the sodium hydroxide solution to combine cleaning with sanitization.
During restrictive inspections, producers of biopharmaceuticals and biological products usually give attention to cleaning and cleaning validation of chromatography resins and multiuse purification systems. Chromatographic resins must either be disposed of or sufficiently cleaned to ensure reproducibility in subsequent cycles.
Over the years, varied cleaning agents have been proposed. Once evaluating a new cleaning agent for a resin, make sure it is compatible with system components as well. Destruction of O-rings and other column components by a cleaning agent is a risk to a process.
For resins, the foremost cleaning agent is sodium hydroxide. Some reports indicate that heated sodium hydroxide is an excellent cleaning agent. Even without the heating, high concentrations of sodium hydroxide require facility and equipment evaluation and use of safety equipment to protect workers.
Sodium hydroxide is frequently used as an industrial cleaning agent where it is often called "caustic". It is added to water, heated, and then used to clean process equipment, storage tanks, etc. It can dissolve grease, oils, fats and protein based deposits. It is also used for cleaning waste discharge pipes under sinks and drains in domestic properties.
As a cleaning agent, sodium hydroxide saponifies fats and dissolves proteins. In general, it can solubilize precipitated proteins. Its hydrolyzing power is enhanced by the presence of chlorine.
Chromatography columns can become contaminated by a variety of protein and nonprotein species during a purification process. Consequences of chromatography column contamination include
- Increase in backpressure
- Loss of signal resolution
- Altered product yield
- Medium discoloration
Common chromatographic contaminants include
- Residual proteins
- Proteins
- Nucleic acids
- Lipids
- Viruses
- Bacteria
- Yeast
- Fungi
- Prions
- Endotoxins
- Metal ions
Sodium hydroxide for proteins removal
Sodium hydroxide has been used extensively to get rid of proteins from ion exchange, hydrophobic interaction, and gel filtration media. The ability of sodium hydroxide to remove proteins from chromatography media depends on the following factors
- Nature of the media
- Nature of sample
- Sample contaminants
These factors may interfere with the cleaning efficiency of sodium hydroxide. A higher concentration of sodium hydroxide may be required if lipids are bound to a protein.
Sodium hydroxide for nucleic acids removal
Nucleic acids can bind tenaciously to anion exchangers of chromatography equipment. 1 M sodium hydroxide and 3 M sodium chloride, with a total contact time of one hour, effectively removes radiolabelled calf thymus DNA from a weak anion exchanger.
Since it is a bacteriostat it is recommended for the removal of bacteria from chromatography equipment sodium hydroxide should be added along with ethanol. Sodium hydroxide may not completely eliminate bacterial spores alone in further good manufacturing process required to complete the process.
Endotoxins are effectively removed by using sodium hydroxide sanitizing agent.
When sodium hydroxide used for sanitization of chromatography media, the ability to withstand stringent sanitizing conditions depends on the following factors
- Functional groups
- Attachment chemistries
- Stability of base matrices to alkaline conditions
Other applications
Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel coloring production, poultry scalding, soft drink processing, and thickening ice cream. Olives are often soaked in sodium hydroxide to soften them, while pretzels and German lye rolls are glazed with a sodium hydroxide solution before baking to make them crisp.
Sodium hydroxide has been used to straighten hair
Reference
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