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Original title: Difference between distilled water, deionized water, reverse osmosis water and ultrapure water 1. Distilled Water Distilled water is the most commonly used pure water in the laboratory. Distilled water can remove most of the contaminants in tap water, but it can't remove volatile impurities such as silica, ammonia, carbon dioxide, and some organic matter. Fresh distilled water is sterile, but after storage, bacteria are easy to reproduce, so it is recommended not to store for a long time. In addition, the container for storing distilled water is also very particular, so it is necessary to choose a container made of non-inert substances as far as possible,thin film distillation, otherwise, the ions and shaping substances in the container will precipitate and cause secondary pollution of distilled water, which can not be used. In the early laboratory, distilled water was widely used because of its convenient preparation. However, although the distilled water equipment is cheap,50l rotovap, it is extremely energy-consuming, water-consuming and slow in water production, and its laboratory application has gradually decreased in recent years. 2. Deionized Water Deionized water is obtained by removing anions and cations from water using an ion exchange resin. There are still soluble organic matters in deionized water, which can pollute the ion exchange column, thus reducing its efficiency and affecting the water quality. Like distilled water, deionized water is also easy to cause bacterial reproduction after storage, so it should be used now to reduce storage time. 3. Reverse osmosis water (Reverse osmosis Water) Reverse osmosis water is a kind of laboratory water which is more and more widely used in laboratory at present. The generation principle of reverse osmosis water is that water molecules produce pure water through reverse osmosis membrane under the action of pressure, and impurities in water are intercepted and discharged by reverse osmosis membrane. The production process of reverse osmosis water has the advantages of low energy consumption, rotovap distillation ,molecular distillation systems, fast water production, safety, pure physical process and no chemical reaction. Therefore, this economical, practical, safe and efficient way of water production is now applied by more and more laboratories. Reverse osmosis water can effectively remove impurities such as dissolved salts, viruses, bacteria, colloids, bacterial endotoxins and most organic substances in water, and overcome many shortcomings of distilled water and deionized water. The desalination rate of a good reverse osmosis membrane can reach about 99%, but reverse osmosis membranes produced by different manufacturers have a great impact on the quality of reverse osmosis water. Because of its high purity, reverse osmosis water is vulnerable to secondary air pollution. Because of its high storage requirements, it should not be exposed to the air for a long time. Ultrapure water equipment 4. Ultra-pure grade water The standard for ultrapure water is water with a resistivity of 18.2 MΩ · cm (25 ℃) (note that we are talking about water in an ideal environment of 25 degrees). In addition to water, the ion content of ultrapure water is close to zero. It is a strong oxidant and is easily polluted by air. Even if it is stored, the resistivity decreases rapidly. Because, in the laboratory, in order to ensure the accuracy of the experiment, we recommend that ultrapure water be used immediately. Ultrapure water is different in TOC, bacteria, endotoxin and other indicators due to the requirements of various experiments. Therefore, it is necessary to determine the relevant standards of ultrapure water according to the requirements of experiments. Several common indexes for evaluating ultrapure water quality are introduced as follows: A. Electrical resistivity, the unit of ultra-pure water resistivity is MΩ/cm (25 ℃), which is an index to measure the conductivity of laboratory water. The resistivity of ultrapure water increases with the decrease of inorganic ions in water, and the resistivity has a reciprocal relationship with the conductivity. Standard for laboratory ultrapure water: the resistivity of water is 18.25 MΩ · cm (25 ℃). B. TOC Total Organic Carbon, TOC is the concentration of carbon in ultrapure water, the unit is ppm or ppb, which can reflect the content of oxidized organic compounds in water, and has a greater impact on some organic experiments. C. Endotoxin,wiped film evaporator, also known as "pyrogen", is mainly the lipopolysaccharide cell wall fragments of Gram-negative bacteria, and its unit is CFU/EU. Ultrapure water for endotoxin removal is mainly used in life sciences. Return to Sohu to see more Responsible Editor:. toptiontech.com