在Purified Water上What are the Likely Organic Impurities in？
The most common organic impurities in purified water are residuals of the more common low molecular weight organics in feed water，organics weakly held on ion-exchange resin and compounds leached from within the water purification system or produced by bacteria within the system.The actual compounds revent。
Where do Organic Impurities come from？
Organic compounds are typically present in the feed water used to supply water purification systems at between1000to3000ppb C（TOC-see below）。Water purification systems are made very largely from plastics to avoid contamination by metals.These can release monomers，release agents etc.if suitable virgin materials are not used.Organics can also be released fromion-exchange（IX）and other media within the purification system。Organics from any or all of these sources will carry over into the product purified water ifthey are not removed effectively。
What Applications do Organic Impurities Affect？
Clearly，the presence in the water of a compound being determined will directly affect the accuracy of the results of analysis.Other compounds with overlapping chromatographic peaks or isotopic masses will also interfere withHPLCand，andLC-MSanalyses respectively.Higher concentrations of less soluble species can lead to degradation in spray characteristics forthese techniques and can degrade column and detector performance in HPLC in Impurities can also affectionisation and form multi-atom ions in ICP-MS and LC-Ms
How are Organic Impurities Monitored？
The only on-line method of monitoring for total organic impurities in purified water is by measuring its total oxidisable carbon content（TOC）。The organics are oxidised（usually by short-wavelength UV light）and a change is monitored。The ELGA in-line TOC monitor measures the change in resistivity of the water to very rapidly determine the TOC.Levels down to 1ppb can be detected.More detailed or sensitive analy be achieved by off-line analysis by，for example HPLC，LC-MS or GC-MS。
What Levels are Important？
The significance of impurities depends on the application.For ultrace analysis even very low（ppb）levels of organics can interfere significantly。TOC of less than5ppb is recommended.For less sensitive analyses higher TOC levels may be acceptable-<10or<50ppb.For historical reasons pharmacopoeia specify<500ppb but many laboratories work to much tighter standards。
How does ELGA Remove Organic Impurities？
To achieve the highest levels of purity with respect to organic impurities ELGA systems uses a combination of technologies.Typically all high molecular weight organics–such as humic and fulvic acids-are removed by high-rejection恢复osmosis（RO）membranes.RO is recommended for the highest purity but for some feed-waters the use of absorption media such asactivated carbonis an alternative
Asubsequent storage reservoir is protected by vent-filtration that absorbs volatile organic compounds.The remaining organics can be removed by recirculation through a dual-wavelengthultravioletchamber.This exposes the water to 185nm UV radiation which oxidises residual organics to ionised species that can be removed by ion-exchange resins and bactericidal254nm UV which minimises the build-up of bacteria and the release of organic degradation products.The purest，high-efficiency mixed bed resins are used throughout to also minimise organic release.The use ofPureSure-twin ion-exchange packs with resistivity monitoring both between the packs and in the product water–makes sure that the first pack is replaced before there is any chance of the second pack becoming less than100%effective。This guarantees that the minimum levels of even weakly retained organicions are achieved and maintained。
