Classification of Laboratory Water Grade Standards

Before we learn about the classification of laboratory water, we need to understand what the commonly used indicators for evaluating water quality are.

1. Electrical resistivity: An indicator of the electrical conductivity of laboratory water, measured in MΩ-cm. As the amount of inorganic ions in the water decreases, the resistance increases, and the value gradually increases. The standard for laboratory ultrapure water is 18.2 MΩ-cm.

2. Total Organic Carbon (TOC): The concentration of carbon in water, reflecting the content of oxidized organic compounds in the water, measured in ppm or ppb.

3. Endotoxin: Lipopolysaccharide cell wall fragments of Gram-negative bacteria, also known as "pyrogens", measured in cuf/ml.

After gaining a thorough understanding of water quality indicators, and classifying them according to their uses, what types of laboratory water can be classified?

I. Common types of water used in laboratories:

1. Distilled Water: The most commonly used type of pure water in laboratories. Although the equipment is inexpensive, it is extremely energy-intensive, water-intensive, and slow, so its use will gradually decrease. Distilled water can remove most contaminants from tap water, but it cannot remove volatile impurities such as carbon dioxide, ammonia, silica, and some organic matter. Fresh distilled water is sterile, but bacteria can easily multiply after storage. In addition, the storage container is also very important; if it is not made of inert material, ions and plastic materials from the container can leach out, causing secondary pollution.

2. Deionized water: Ion exchange resins are used to remove anions and cations from water. However, soluble organic matter still exists in the water, which can contaminate the ion exchange column and reduce its effectiveness. Deionized water is also prone to bacterial growth after storage.

3. Reverse osmosis water: Its production principle involves water molecules being forced through a reverse osmosis membrane under pressure to become pure water, while impurities are retained and discharged. Reverse osmosis water overcomes many shortcomings of distilled and deionized water. It effectively removes dissolved salts, colloids, bacteria, viruses, bacterial endotoxins, and most organic matter from water. However, the quality of reverse osmosis water is greatly affected by the type of reverse osmosis membrane produced by different manufacturers.

4. Ultrapure water: The standard for ultrapure water is a resistivity of 18.2 MΩ-cm. However, ultrapure water varies in terms of TOC, bacteria, endotoxins, etc., and the specific requirements must be determined based on the experimental requirements. For example, cell culture has requirements for bacteria and endotoxins, while HPLC requires low TOC.

II. According to the GB6682-2008 standard, what are the different categories of pure water quality?

According to the GB6682-2008 water standard, pure water quality can be classified into the following three categories:

(1) Grade III water standard, resistivity 0.2 MΩ.cm @ 25℃;

(2) Grade II water standard, resistivity ≥ 1 MΩ·cm @ 25℃;

(3) Grade I water standard, resistivity ≥ 18.25 MΩ·cm @ 25℃. Specific technical indicators are as follows:

What are the application areas for different levels of pure water?