Thread Content
With the advancement of technology, laboratory instruments are becoming increasingly precise, and the requirements for reagents and water used in testing processes are also rising. Lab water, which is essential everywhere in the experimental process, is particularly important. So, how much do you know about some basic facts regarding water used in laboratories? 1 Distilled Water: Distilled water is the most commonly used type of pure water in laboratories. Distilled water can remove most of the pollutants from tap water, but it cannot eliminate volatile impurities such as silica, ammonia, carbon dioxide, and certain organic compounds. Fresh distilled water is sterile, but bacteria can easily multiply after storage; therefore, it is recommended not to store it for long periods of time. Additionally, the containers used for storing distilled water also need to be carefully chosen; it is best to use containers made of non-inert materials. Otherwise, ions and plasticizing substances in the container can leach out, causing secondary contamination of the distilled water and rendering it unusable. In early laboratories, it was widely used because distilled water was easy to prepare. However, although distillation water equipment is inexpensive, it is extremely energy-consuming, uses a lot of water, and has a slow water production rate; as a result, its use in laboratories has been decreasing in recent years. 2 Deionized Water: Deionized water is obtained by using ion exchange resins to remove anions and cations from water. Soluble organic substances are still present in deionized water, and they can contaminate the ion exchange columns, thereby reducing their efficiency and affecting water quality. Just like distilled water, deionized water can also facilitate bacterial growth when stored, so it should be used as soon as it is prepared to minimize storage time. 3 Reverse osmosis water: Reverse osmosis water is a type of laboratory water that is being used more and more frequently in laboratories these days. The principle behind the production of reverse osmosis water is that water molecules, under pressure, pass through a reverse osmosis membrane to produce pure water, with impurities in the water being trapped by the membrane and removed. The production process of reverse osmosis water is energy-efficient, fast, and safe; it is a purely physical process with no chemical reactions. Therefore, this economical, practical, safe, and efficient water production method is now being adopted by an increasing number of laboratories. Reverse osmosis water can effectively remove impurities such as dissolved salts, viruses, bacteria, colloids, bacterial endotoxins, and most organic substances from water, overcoming many of the drawbacks of distilled water and deionized water. High-quality reverse osmosis membranes can achieve a desalination rate of around 99%, but the quality of the reverse osmosis water is greatly influenced by the membranes produced by different manufacturers. Due to its high purity, reverse osmosis water is prone to secondary contamination by air; given the stringent storage requirements, it should be kept out of the air for as short a time as possible. 4 Ultra-pure water: The standard for ultra-pure water is a resistivity of 18.2 MΩ·cm at 25°C (please note that the conditions referred to here apply to water under ideal conditions of 25 degrees Celsius). Ultra-pure water contains almost no ions other than water; it is a strong oxidizing agent that is highly susceptible to secondary contamination by air. Even when stored, its resistivity decreases rapidly. Because, in the laboratory, to ensure the accuracy of experiments, we recommend using ultrapure water immediately after it is prepared. The requirements for ultrapure water in terms of indicators such as TOC, bacteria, and endotoxins vary depending on the needs of various experiments; therefore, it is necessary to determine the relevant standards for ultrapure water based on those experimental requirements. The following are several common indicators used to evaluate the quality of ultrapure water: A. Electrical resistivity – the unit for the resistivity of ultrapure water is MΩ/cm at 25°C, and it is an indicator used to measure the electrical conductivity of water used in laboratories. The resistivity of ultrapure water increases as the amount of inorganic ions in the water decreases; resistivity and conductivity are inversely related to each other. Standard for ultra-pure water in the laboratory: The resistivity of the water is 18.25 MΩ·cm (at 25°C). B. TOC – Total Organic Carbon. TOC represents the concentration of carbon in ultrapure water, expressed in ppm or ppb. It indicates the amount of oxidized organic compounds present in the water, and it has a significant impact on certain organic compound experiments. C. Endotoxin: Also known as “pyrogen,” endotoxin is primarily a fragment of the lipopolysaccharide cell wall found in Gram-negative bacteria. It is expressed in units of CFU/EU. Ultra-pure water free of endotoxins is mainly used in life sciences.