Application and preparation of pure water and ultrapure water
With the advancement of science and technology, people’s understanding of all kinds of things in nature has evolved toward microcosm and essentialization. Many experiments and detections require reagents or impurities in the culture environment to reach the ppb level. It even reaches ppt level; for example, in the life science research process, it is very sensitive to many pollutants in water, especially heavy metals and soluble organic matter; ultra-pure water required in HPLC, and so on. In light 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 “Specifications and Experimental Methods of Water for Analytical Laboratories”, National Standard of the People’s Republic of China GB / T11446.1-1997 “Specifications and Experimental Methods of Electronic Grade Water”, American Chemical Society Organization (ACS), American Society for Testing and Materials Experimentation (ASTM), International Committee for Standards in Clinical Trials (NCCLS), American Pharmaceutical Association (USP). Here we first make a brief introduction to the main applications of pure water and ultrapure water:
1. Pure reverse osmosis water:
① final cleaning of laboratory utensils ② water for buffer solution and chemical reagent preparation ③ water for preparation of microbial culture medium ④ pure water for hydrogen generator, indoor humidifier, autoclave ⑤ drinking water for human or experimental animals Wait;
2. Ultrapure water:
① Water for animal and plant fine cell culture ② Water for various medical biochemical analyzers, analyzers, hemodialyzers ③ Analytical reagents and drug configuration dilution water ④ Physiological, pathological, and toxicological experimental water ⑤ Hospitals, medicine Purified water and high-purity water for preparation room and central laboratory ⑥ Water for atomic absorption spectroscopy ⑧ Water for test tube babies ⑨ Various HPLC, ion chromatographic water ⑨ Other various laboratory and medical water.
At present, the most stable and convenient method for preparing pure water and ultrapure 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 the ultrapure water system has been constantly revolving around “the best water quality and 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. Pure water / ultra-pure water systems are designed to remove these impurities as thoroughly as possible.
2. The main process of water purification
At present, the commonly used processes for purifying water include distillation, reverse osmosis, ion exchange, filtration, adsorption, and ultraviolet oxidation. At the same time, we can roughly divide the purification process of water into 3 major steps, pre-treatment (to produce pure water), ion exchange (to produce 18.2 MΩ-cm ultra-pure water) and post-treatment (to produce ultra-pure water that meets special requirements). water). According to the quality of the incoming water and the requirements for the quality of the outgoing water, determine the method and process used at each step.
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 including large particulate matter, residual Chlorine and calcium ions and magnesium ions. The point to be explained here is that different processing units must be specifically equipped according to the differences in the quality of the incoming water. Most pure water instrument manufacturers do not help customers solve this problem well, which will lead to subsequent purification failure to achieve the desired results and shorten the life of major components such as reverse osmosis membranes.
Reverse osmosis is to use a high pressure pump to provide high concentration solution with a pressure greater than the osmotic pressure difference. Water molecules will be forced to pass through the semi-permeable membrane to a low concentration side. Reverse osmosis can remove 90% -99% of inorganic ions including Most of the pollutants in it are because of its superior purification efficiency. Reverse osmosis is a very effective technology for water purification systems. Because reverse osmosis can remove most of the pollutants, it is often used as a front treatment method. Can significantly extend the use of deionization columns. Since reverse osmosis is very critical in the water purification process and the replacement price of the reverse osmosis membrane is high, we recommend that users must choose an ultrapure water system that has a protective function for the reverse osmosis membrane.
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 is the exchange of positive ions in water with H + ions in the ion exchange resin, and negative ions in water with OH- ions on the ion exchange resin, so as to achieve the purpose of purifying water. Removal of ions by ion exchange can theoretically remove almost all ionic substances. At 25 ° C, the effluent resistivity reaches 18.2MΩ-cm. The quality of the effluent 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 with fish and dragons, the quality is uneven, and it is difficult for users to distinguish. So we recommend that users pay attention to the brand of resin.
It should be noted here that the ion exchange method can effectively remove ions, but it cannot effectively remove most of the organic matter or microorganisms. The microorganisms can be attached to the resin, and the resin is used as a 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 that we will discuss below.
According to the special requirements of customers, ultra-pure water of low organic matter type and low heat source type is produced. There are various treatment methods for different requirements, such as ultrafiltration filtration method to remove heat sources, dual-wavelength ultraviolet oxidation method to reduce total organic carbon (TOC) in water, and microfiltration to remove bacteria.
Ultrafiltration (UF) membrane is a molecular sieve. It is based on size and allows the solution to pass through a very fine filter membrane to achieve the purpose of separating molecules of different sizes in the solution. The heat source content in ultrapure water can be reduced to 0.001 EU. / 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 5 ppb.
the most stable water quality
The ultra-pure water system can produce high-quality ultra-pure water is only the first step. For the user, it is the user’s most concern that it can maintain the high effluent water quality as long as possible. At present, most manufacturers emphasize that customers pay attention to the details of use and often change parts and consumables, but there are not many improvements made on their own.