The 491M/B/SD Gas Standards Generator, from Kin-Tek Laboratories Inc., dynamically blends precisely known gas standards with parts-per-trillion (ppt) analyte concentrations. The system uses two stages of dilution to achieve ppt concentrations. The first stage combines the emission of analyte vapor from a Trace SourceTM permeation tube with a precisely known flow of pure dilution gas to form a parts-per-billion concentration primary mixture. In the second stage an aliquot of the primary mixture is further diluted to form the ppt mixture. Suitable permeation tubes are available for over 400 compounds.
The 491M/B/SDcircumvents several common problems with ppt standards. First, for most compounds, ppt and even ppb gas standards are not stable in storage due to reactions and adsorption by the container. With direct blending methods the key problems are measuring the analyte flow and obtaining true "zero gas" for use as diluent. By using two independent stages of dilution the 491M/B/SD allow ppt standards to be created from analyte flow rates above 10 nl/min with total dilution gas flow less than 20 l/min. To insure accuracy in spite of significant contamination of the dilution gas the system can make "standard additions" to the dilution gas to allow compensation for unknown contamination.
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