Title Does Your Lab Require Low Toc Water Purification
Pure water is a commodity in many industries in particular in analytical and biologic laboratories. Laboratory grade water is defined by its resistivity, which is dependent upon the amount of ionic contaminations and by its Total Organic Carbon content (TOC). Resistivity of the water determines the water quality based on American Society for Testing and Material (ASTM) definitions. Many routine laboratory applications use ASTM Type II water with a resistivity of >1M/cm2 which corresponds to less than 500ppb total ionic contamination. More specialized applications in analytical chemistry and molecular and cell biology require water of ASTM Type I with a resistivity of >18 M/cm2 which corresponds to about 1ppb total ionic contaminations in the water. ASTM water quality definitions do not give any information regarding the amount of organic compounds in the water. Organic compounds, however, could cause serious problems for several analytical chemistry and biological applications. Liquid phases and buffers prepared for HPLC have to have ultralow TOC and ultralow ionic contamination, as these contaminants can arrive as split up peaks in the chromatogram and also increase background and decrease sensitivity. These same holds true for gas chromatography (GC), Atomic Absorption Spectroscopy (AAS), Ion Chromatography (IC), Electromagnetic Spectroscopy, and mass spectrometry (MS). Several molecular biology applications require water that is not only ASTM Type I, but additionally nuclease- and pyrogen-free, which can be most reliably achieved with ultra-pure water with ultra-low TOC. Electrophoresis, polymerase chain reaction, DNA and RNA extraction and other methods that use nucleic acids need water that’s nuclease-free to avoid degradation of the DNA. Because of the stability and abundance of RNAses as contaminants, a source of water that’s nuclease-free is even more important for applications that use RNA. Enzyme Linked Immuno-Sorbent Assays (ELISAs) can detect minute levels of specific contaminants that can increase background and decrease sensitivity of the assay. Many analytical assays that use fluorescence for detection also need low TOC as many organic compound fluoresce somewhat in UV light. Cell biology is another area where low TOC and purity of water is crucial. Water used for the preparation of buffers and media for tissue culture does not only have to be sterile (free of microbes like bacteria and viruses), but additionally free of organic contaminants like endotoxin. Endotoxin contaminations in tissue culture can restrict cell growth, cytokine responses and significantly alter the results of experiments. Drug preparations intended for the utilization in animals or humans also need to be manufactured with high-quality ultra-pure, ultralow TOC, and endotoxin-free water, as endotoxin cannot only alter link between in vivo experiments dramatically, however it may even cause toxicity, though endotoxin contaminations at a level that can cause toxicity are rare. FDA requirements for human and veterinary medications restrict the usage of water for production of medications to the highest purities. To purify plain tap water to ASTM type I and ultra-low TOC standards, purification systems are employed that employ a number of different purification methods, all of which has different maintenance requirements. An important part of any water purification system that’s likely to achieve ASTM Type I grade purity is a deionizing system. A deionizer removes cationic contaminants in trade for H+ ions and anionic contaminants in trade for OH- ions. The purity of the water is dependent upon the caliber of the ion exchange resin used and the caliber of the maintenance of the system. Ion exchange resins have a limited capacity of ions they could exchange and have to be replaced once they reach their limit. The resin may be regenerated, however the regeneration process can affect the resin which can lead to organic contaminations. Ion exchangers usually do not reduce microbial contaminations, and bacteria can accumulate within the resin, resulting in a lot of endotoxin within the resin. Virgin ion exchange cartridges, i. e. cartridges with new rather than regenerated ion exchange resin are usually used for the greatest purity water. UV-sterilized feed water prevents the buildup of bacteria. Most lab water purification systems that produce ASTM Type I water use feed water that’s already lower in contaminants than plain tap water. Pretreatment using activated charcoal can remove chlorine and, to a certain extend, organic compounds from plain tap water and reverse osmosis is a very reasonable solution to reduce about 95% of most contaminants, rendering it an extremely useful pretreatment for feed water for ASTM Type I purifiers. reverse osmosis water filtration may be damaged by CaCO3 deposits and deposits of organic compounds and colloids. Water softeners and pretreatment of the water with activated charcoal can significantly raise the live of the reverse osmosis unit. Since ion exchangers cannot remove non-charged organic compounds, these have to be removed in a split up step. Different filtration steps will remove, with regards to the cutoff of the filtration membrane, starting from large particles, bacteria and viruses, down to endotoxin and nucleases. However, while microporous filters like e. g. the people used for removing bacteria with a cutoff of 0. 2 micron can remove 100% of particles above the cutoff diameter, ultrafiltration filters that are used for smaller particles and organic compounds like endotoxin and nucleases remove most, but not all contaminants above the cutoff diameter. Both microporous filters and ultrafiltration membranes can clog when to many contaminants are deposited on top. If this happens they have to be replaced. Ultrafiltration membranes clog much easier than microporous filters, so that they are usually placed behind other filtration steps in a water purification system. To help reduce TOC a UV-oxidizer needs to be used. Since UV oxidizers increase the amount of dissolved ions and for that reason reduce resistivity in the water, the most logical position of a UV-oxidizer in a lab water purification system is before the deionzing step that produced water with high resistivity. The UV-oxidizer also sterilizes the water reducing the danger of bacterial contamination of the subsequent ion-exchanger resin in this configuration. The low pressure mercury lamps in UV-oxidizers/sterilizers have a limited life span and have to be replaced every so often. In several systems another ultrafiltration step can be used at the very end to guarantee the sterility of the water.