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Nearly all assays on modern clinical analyzers are run at 37 °C. Purified water used by the analyzer will also have its temperature increased to 37 °C. Tap water feeding a water purification system can be at temperatures as low as 5 °C to 10 °C. As the temperature of this water is increased to 37 °C, dissolved gases which were soluble at the colder tap water temperatures become insoluble and can form bubbles within the tubing and on the optical surfaces of the analyzer. These bubbles can interfere with the analyzer’s optical measurements and, in some instruments, can reduce the precision of dispensed volumes of water which may ultimately impact test results. Some analyzers actually require small amounts of dissolved oxygen in the water as a reactant for certain assays. In these analyzers it is necessary to control the amount of dissolved gasses without reaching the solubility limit of the gases in the water. The AFS degassing option employs a patented degassing technology which controls the level of degassing to optimize the analyzer’s performance while eliminating the chance of bubble formation in tubing, near optical sensors, and in water baths within the analyzer, thus assuring maximum precision of the assays performed on the analyzer.

A quotation from the current NCCLS document covering water quality for the clinical laboratory summarizes the need for low silica levels in reagent water. 9.5 Soluble Silica “Silica can affect most enzyme determinations, as well as trace metal and electrolyte analyses. At high concentrations, silica can also directly interfere with some spectrophotometric measurements.” Source: "Preparation and Testing of Reagent Water in the Clinical Laboratory," Third Edition, NCCLS Document C3-A3 Vol. 17 No. 18, October 1997.

All AFS units combine state-of-the-art water purification technologies that allow for production of NCCLS/CAP Type I/Type II water directly from tap water. Reverse osmosis (RO) is used as an initial purification step. RO removes nearly all bacteria, colloidal silica, particulates, organics and a large percentage of ionic contaminants from the feed water. Water which permeates the RO membrane still contains small amounts of contaminants and will not meet NCCLS/CAP Type I or Type II specifications. As water is demanded by the analyzer, the AFS automatically supplies stored RO water to a high purity AFS polishing pack which contains the strongest and cleanest type of ion exchange resin currently available. This resin “polishes” the water to meet Type I resistivity and silica specifications. The final purification step is accomplished using a filter device with a pore size rating of 0.22 microns, or less, which ensures absolute bacteria retention. At this point, all NCCLS Type I and Type II specifications can be guaranteed and the water is delivered to the analyzer.