Introduction to Laboratory Water Standards

Water used in experiments has specific requirements for water quality depending on the different experimental purposes, such as instrument cleaning, solution preparation, chemical reactions and analyses, and biological tissue culture. Natural water often contains impurities such as sodium, calcium, magnesium carbonates, sulfates, sand, chlorides, organic matter, and microorganisms, which do not meet the requirements for laboratory experiments. Therefore, water needs to be purified, and pure water is typically obtained using methods such as reverse osmosis, continuous electro-deionization, and ion exchange.

Preparation of Pure Water by Ion Exchange

Pure water prepared by ion exchange is commonly known as “deionized water” or “ion-free water.” The use of ion exchange to produce pure water has high water purity, and simple operation, and has been widely adopted in laboratories with the necessary lab water purification equipment.

Classification of Laboratory Pure Water

Classification of Laboratory Pure Water(1)

  1. Deionized water: Ion exchange resins are used to remove anions and cations from water, but there are still soluble organic compounds that can contaminate the ion exchange column, reducing its effectiveness. Stored deionized water can also easily promote bacterial growth.
  2. Reverse osmosis water: Reverse osmosis water overcomes many of the shortcomings of distilled water and deionized water. The use of reverse osmosis technology can effectively remove particles, colloids, organic impurities, heavy metal ions, bacteria, viruses, and 99% of dissolved salts from water.
  3. Ultra-pure water: Ultra-pure water has different indicators in terms of TOC, bacteria, and endotoxins, depending on the requirements of the experiment. For example, cell culture requires low bacteria and endotoxin levels, while HPLC requires low TOC levels.

Classification and Standards of Laboratory Pure Water

The national laboratory pure water standard (GB/T 6682) divides water into three levels based on water purity (water conductivity): Level 1 with a conductivity of less than 0.1μs/cm, Level 2 with a conductivity of less than 1.0μs/cm, and Level 3 with a conductivity of less than 5.0μs/cm.

Level 3 water is laboratory-grade pure water, recommended for glassware washing, water baths, high-pressure sterilization, and ultra-pure water system inlet water.

Classification and Standards of Laboratory Pure Water(1)

Level 2 water is generally used for routine laboratory applications, such as buffer solutions, pH solutions, and microbial culture medium preparation, supplying water to ultra-pure water systems, clinical biochemical analyzers, incubators, and aging machines, and can also be used for chemical analysis or synthetic reagent preparation.

Level 1 water is often used for strict experimental applications, such as HPLC mobile phase preparation, GC blank sample preparation and sample dilution, high-precision analysis techniques such as HPLC, AA, ICP-MS, buffer solution, mammalian culture medium preparation, test tube babies, molecular biology reagent preparation (DNA sequencing, PCR amplification, etc.), electrophoresis, and hybridization solution preparation, etc.

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