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