ASSURING TRACEABLE ACCURACY OF TRACE CONCENTRATION GAS STANDARDS

摘要

Regulated monitoring (environmental, pharmaceutical, etc.), legal considerations in workplace monitoring, and all of the documented quality assurance programs require accuracy of analytical measurements be traceable to national standards. Currently there are over 500 compounds of environmental and/or industrial interest that are measured as vapors at trace (ppm, ppb, or ppt) concentrations. Yet there are less than 50 compounds for which there are trace level vapor reference standards. Establishing calibration accuracy for the other 400+ compounds is a significant problem. Traceability of trace vapor mixtures to the National Institute of Standards and Technology (NIST) can often be established through fundamental physical standards. This paper compares several dynamic blending techniques based on fundamental measurements, defines the known error sources of each and describes methods for estimating the accuracy of mixtures produced.