Purified water is water that has been physically processed using a water purification device to remove impurities. There are a considerable number of methods and devices that can be used for this purpose.
While distillation and deionization are the most common, there are a number of other methods in use. These include reverse osmosis, carbon filtration, microporous filtration, ultrafiltration, ultraviolet oxidation or electrodialysis. Various filters are used in most of these processes. A combination of some of processes is sometimes utilized to produce water of such high purity that its levels of trace contaminants are measured in parts per billion (ppb) or even parts per trillion (ppt). Highly purified water such as this is often used in laboratories and in engineering applications.
A water purification device or system is used to produce potable drinking water as well as to produce purified water for use in the lab. Some of these devices are employed in specific fields or for unique purposes. A purification device that is used in basic chemistry applications is categorized by purity level.
These equipment purity levels include basic, low organic, pyrogen-free and low organic/pyrogen-free combination units. To produce Type I laboratory grade water with very low levels of dissolved organic contamination, a laboratory water polishing system using ultraviolet light can be utilized. To obtain Type I laboratory grade water for pyrogen-free, endotoxin-free and Rnase-free applications, a water purification device with ultrafiltration is used. Ultrafiltration is often used instead of a microporous filter, since it is particularly effective in the removal of particulates, microorganisms and pyrogens.
This makes it the companion filter of choice whenever pharmaceutical applications are involved. This type of system performs best when it is fed with water that has been pretreated by reverse osmosis or deionization. Laboratory water that is to be used for ultrapure applications, such as those requiring ultra low organic and pyrogen-free Type I laboratory grade water, utilize water polishing systems that combine all of the technologies used in the previous methods. These water purification devices use activated carbon, deionization, ultraviolet oxidation, ultrafiltration and 0.22 micron filtration. They also perform best when fed with water that has been treated by reverse osmosis or deionization.
Filtration as a water purification method can be divided into five types. Particle filtration can include anything from a coarse sand filter, with an effective pore size greater than 1,000 microns, to a cartridge filter with a pore size of 1 micron or greater. Microfiltration, which is also known as sub-micron filtration, includes filter devices with pore sizes ranging from just under 1 micron to about 0.05 micron. Bacteria, which range from about 0.2 to 30 microns in diameter, can actually be removed from water and other liquids using microfiltration at the 0.2 micron level.
Some water purification devices employ ultrafiltration; this is essentially a membrane filter or molecular sieve that can remove molecules from water that have a diameter larger than about 0.003 micron. A virus, pyrogen, endotoxin, R-Nase and D-Nase can be removed from water by using ultrafiltration. Nanofiltration fills the space between ultrafiltration and reverse osmosis, with an effective pore size of 0.001 to 0.01 micron though it actually serves no useful purpose in the field of water purification. Reverse osmosis membrane filters have a pore size of less than 0.001 micron. This allows them to separate individual ions from a solution.
Final filtration is an integral part of every laboratory water purification device. Submicron capsule filters are generally the final step in the purification process. A 0.2 micron filter is most commonly used to remove bacteria before dispensing the final product water. Finer capsule filters are sometimes used to remove pyrogens and nucleases. Capsule filters will restrict the flow rate at which water is produced, but the quality of the final product make these filters an integral part of an exceptionally effective water purification system.
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