Twenty-five years ago, water was considered "pure" enough for laboratory use if it would resist electrical current fairly well, suggesting it was relatively free of conductive ions. A new generation of highly sensitive analytical instruments-including high-performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS)- demand ultrapure water. Today's purification systems eliminate most contaminants, delivering water with total organic carbon (TOC) levels lower than a few parts per billion, inorganic contamination in the 50 parts-per-trillion range, and resistivity better than 18 megohms per centimeter.

ADVANCED LINE: The WaterPro Reverse Osmosis system, distributed by Labconco.
The most advanced water purification systems also eliminate bacteria, bacterial fragments known as pyrogens, and even enzymes such as RNase. At the Fairfax Medical Lab in Chantilly, Va., for example, researcher Tony Cooper feeds ultrapure water into a chemistry analyzer whenever he measures liver enzymes, electrolytes, proteins, and other constituents in blood samples....

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