subject: What Makes Laboratory Grade Water Different? [print this page] A variety of contaminants and impurities which may be present in water supplies. Laboratory grade water is water which has had impurities such as microorganisms, particulates, dissolved ionized or non-ionized solids and gases as well as endotoxins, pyrogens, DNase and RNase to make it suitable for use in the laboratory. Pure water is a necessity in all laboratories, though different applications call for different degrees of purification. Broadly speaking, there are three different grades of laboratory water (four using the standards for laboratory water as defined by the American Society for Testing and Materials). These grades of lab water being designated as types one through four.
Type I water is ultrapurified water which has a nearly nonexistent level of particulate matter, bacteria and other microorganisms, organic carbon (measured in terms of total organic carbon or TOC),endotoxins, pyrogens and other contaminants. Type one laboratory grade water is typically produced by first purified through deionization, distillation or osmosis before undergoing further purification. This grade is also referred to as analytical grade water and is used for applications including in vitro fertilization, HPLC, ion chromatography and tissue culture.
Type II water contains very low amounts of colloids, organic and inorganic impurities; low enough to make this grade usable in trace analysis, atomic absorption spectrometry and other analytical applications whose sensitivity demands a high degree of water purity. Type II water can be produced by purifying potable water (such as tap water) using reverse osmosis in conjunction with distillation, ion exchange or multiple distillation.
Type III laboratory grade water is characterized by low levels of contaminants as well as levels of conductivity and resistance which make it suitable for use in a wide variety of routine applications. Type III water is used for preparing reagents in solutions, preparing chemical buffers and a range of wet chemistry work and is the standard water used for analytical purposes in laboratories. This general grade of laboratory water is also used in microbiological studies and preparing nutrient media for cell culture. Type III water may be produced through commercially available water purification equipment which uses several different purification methods or by double distillation.
Laboratory grade water may be produced by a number of methods: Filtration technologies including reverse osmosis, nano, ultra, micro and particle filtration may all be used to remove particulates and other contaminants to produce water which is pure enough for laboratory use. Filtration is often the first step in producing type I and II water.
UV radiation is useful for eliminating bacteria and other microorganisms in water, though this purification method does not remove particulate matter or produce water with the pH or conductivity levels required for some applications. UV light is often used in conjunction with filtration or other purification methods to produce laboratory grade water, such as distillation, deionization filtration and activated carbon adsorption.
Even for some of the most routine tasks in laboratories such as rinsing and washing glassware, the purity of the water used matters. For sensitive applications, any water used must be purified in order to eliminate the possibility of contamination or reactions which can influence the outcome of a process and make the results unreliable. Even the smallest impurities can have a serious effect, making pure water an important concern in the laboratory.
