Laboratory water common sense
Water is an often overlooked but vital reagent in the laboratory. What types of laboratory water are there? What level can I reach? What are the water requirements for different experiments? To clarify these vague concepts, repost this post.
Common types of water in the laboratory:
1. Distilled Water:
The most commonly used type of pure water in the laboratory, although the equipment is cheap, is extremely energy and water consuming and slow, and the application will gradually decrease. Distilled water can remove most of the pollutants in tap water, but volatile impurities cannot be removed, such as carbon dioxide, ammonia, silica and some organics. Fresh distilled water is sterile, but bacteria can easily multiply after storage. In addition, the storage container is also very particular. If it is a non-inert substance, ions and plastic molding materials will precipitate and cause secondary pollution.
2. Deionized Water:
Ion exchange resin is used to remove anions and cations in water, but soluble organic matter still exists in the water, which can contaminate the ion exchange column and reduce its efficacy. Deionized water can easily cause bacteria to multiply after storage.
3. Reverse osmosis Water:
The principle is that water molecules become pure water through the reverse osmosis membrane under the action of pressure, and impurities in the water are trapped and discharged by the reverse osmosis membrane. Reverse osmosis water overcomes many shortcomings of distilled water and deionized water. The use of reverse osmosis technology can effectively remove dissolved salts, colloids, bacteria, viruses, bacterial endotoxins and most organic impurities in water. It has a great impact on the quality of reverse osmosis water.
4. Ultra-pure grade water:
The standard is water resistivity of 18.2 MΩ cm. However, ultrapure water is not the same in terms of TOC, bacteria, endotoxin and other indicators. It must be determined according to experimental requirements. For example, cell culture requires bacteria and endotoxin, and HPLC requires low TOC.
Common indicators for evaluating water quality:
1. Electrical resistivity:
The index to measure the conductivity of laboratory water, the unit is MΩ cm. As the resistance of the inorganic ions in the water decreases, the value gradually increases. The standard of laboratory ultrapure water: the resistivity is 18.2MΩ cm.
2. Total Organic Carbon (TOC):
The concentration of carbon in water reflects the content of oxidized organic compounds in water. The unit is ppm or ppb.
Fragment of lipopolysaccharide cell wall of gram-negative bacteria, also called "pyrogen", unit is cuf / ml.