Application and preparation of pure water ultrapure water

With the advancement of science and technology, people’s understanding of all kinds of things in nature is moving towards microscopic and essential development. Many experiments and tests require reagents or impurities in the culture environment to reach the ppb level, and some It can even reach the ppt level; for example, in the process of life science research, it is very sensitive to a variety of pollutants in water, especially heavy metals and soluble organics; ultra-pure water required by HPLC, etc. In view of this, a number of professional research organizations have established water quality standards. These organizations and standards are: National Standard of the People’s Republic of China GB6682-92 “Analytical Laboratory Water Specifications and Experimental Methods”, National Standard of the People’s Republic of China GB/T11446.1-1997 “Electronic Grade Water Specifications and Experimental Methods”, American Chemical Society Organization (ACS), American Society for Testing and Materials Experimentation (ASTM), American International Committee on Clinical Trial Standards (NCCLS), American Pharmaceutical Society (USP). Here we first give a brief introduction to the main applications of pure water and ultrapure water:

1. Reverse osmosis pure water: ① Final cleaning of laboratory utensils ② Buffer and chemical reagent preparation water ③ Microbial culture medium preparation water ④ Pure water for hydrogen generator, indoor humidifier, autoclave ⑤ Drinking water for human or laboratory animals Wait;

2. Ultrapure water: ① Water for animal and plant cell culture ② Water for various medical biochemical instruments, analyzers, hemodialysis machines ③ Water for dilution of analysis reagents and medicines ④ Water for physiology, pathology, toxicology experiments ⑤ Hospital, medicine Purified water and high-purity water for preparation room and central laboratory ⑥ Water for atomic absorption spectrometry ⑦ Water for test tube babies ⑧ Water for various high performance liquid chromatography and ion chromatography ⑨ Water for other various laboratories and medicines.

At present, the most stable and convenient method for preparing pure water and ultra-pure water is through a pure water/ultra-pure water system. From the advent of the world’s first ultrapure water system to the present, the design and production concept of ultrapure water system has been continuously improved around “the best water quality, the most stable water quality”.

The best water quality

1. Common impurities in natural water

Including soluble inorganic matter, organic matter, particulate matter, microorganisms, soluble gas, etc. The pure water/ultra pure water system is to remove these impurities as thoroughly as possible.

2. The main process of purifying water quality

At present, the commonly used process methods for water purification include distillation, reverse osmosis, ion exchange, filtration, adsorption, and ultraviolet oxidation. At the same time, we can roughly divide the water purification process into 3 major steps, pre-treatment (to produce pure water), ion exchange (to produce 18.2MΩ-cm ultra-pure water) and post-treatment (to produce ultra-pure water that meets special requirements). water). According to the water quality of the influent and the requirements for the quality of the effluent, determine the method and technology used in each step.

3. Pretreatment

It mainly includes a pretreatment unit and a reverse osmosis (RO) unit. Since the pretreated water will be further purified by reverse osmosis, it is necessary to remove impurities that affect the reverse osmosis membrane as much as possible; mainly include large particulate matter, residual Chlorine and calcium ion and magnesium ion. The point to be explained here is that different treatment units must be equipped according to the difference in water quality. Most water purification instrument manufacturers cannot help customers solve this problem well, which will cause the subsequent purification to fail to achieve the desired results and shorten the life of the main components of the instrument such as reverse osmosis membranes.
Reverse osmosis uses a high-pressure pump to provide a higher pressure difference than the osmotic pressure for a high-concentration solution. Water molecules will be forced to pass through a semi-permeable membrane to the low-concentration side. Reverse osmosis can filter out 90%-99% of inorganic ions. Most of the pollutants inside, because of its outstanding purification efficiency, reverse osmosis is a very effective technology for water purification systems. Because reverse osmosis can remove most of the dirt, it is often used as a pre-treatment method. Can significantly extend the use time of the deionization exchange column. In view of the fact that reverse osmosis is very critical in the water purification process and the replacement price of reverse osmosis membranes is relatively high, we recommend that users must choose an ultrapure water system that has a protective function for reverse osmosis membranes.
In order to extend the service life of the reverse osmosis membrane as much as possible and improve the filtration efficiency of the reverse osmosis membrane

4. Ion exchange

Ion exchange means that the positive ions in the water are exchanged with the H+ ions in the ion exchange resin, and the negative ions in the water are exchanged with the OH- ions on the ion exchange resin to achieve the purpose of purifying water. By removing ions through ion exchange, almost all ionic substances can be removed theoretically. At 25°C, the resistivity of the effluent reaches 18.2MΩ-cm. The quality of the water after ion exchange mainly depends on the quality of the ion exchange resin and the exchange efficiency of water and resin in the exchange column.
Ion exchange resins on the market are mixed, and the quality is uneven, making it difficult for users to distinguish. Therefore, we suggest that users must pay attention to the brand of resin.
It should be noted here that the ion exchange method can effectively remove ions, but cannot effectively remove most of the organic matter or microorganisms. The microorganisms can be attached to the resin and the resin is used as the culture medium, so that the microorganisms can grow quickly and generate heat. Therefore, it needs to be designed and used in conjunction with other purification methods, which is the post-processing part we will discuss below.

5. Post-processing

It mainly produces ultra-pure water with low organic matter type and low heat source type according to the special requirements of customers. There are a variety of treatment methods for different requirements, such as ultrafiltration filtration to remove heat sources, dual-wavelength ultraviolet oxidation to reduce total organic carbon (TOC) in water, and microfiltration to remove bacteria.
Ultrafiltration (UF) membrane is a molecular sieve, which is based on the size, allowing the solution to pass through a very fine filter membrane to achieve the purpose of separating molecules of different sizes in the solution, which can reduce the heat source content in the ultrapure water to 0.001EU /ml or less. The dual-wavelength ultraviolet oxidation method can use photo-oxidation of organic compounds to reduce the total organic carbon concentration in ultrapure water to less than 5ppb.

The most stable water quality

The ability of ultrapure water systems to produce high-quality ultrapure water is only the first step. For users, it is the most concerned issue for users to maintain high water quality as long as possible. At present, most manufacturers emphasize that customers should pay attention to details and often change accessories and consumables, but they have not made many improvements on their own.

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