Outside of laboratory conditions, surrogate gas calibration for chlorine dioxide is recommended because it can be difficult to generate a stable source of ClO2, Indeed, the use of chlorine as a surrogate for chlorine dioxide calibration is one of the very few instances whereby Interscan gives limited support to such a method.
Indeed permeation devices are available for chlorine, but not chlorine dioxide. However, calibration devices for ClO2 are available from Advanced Calibration Designs, Inc.
Still, the caveats detailed in our article covering surrogate calibration are very much in effect. Our limited endorsement in this particular case occurs only because a highly respected third party has performed the validation. Notably, this was done out of necessity, since at the time, the ACD devices were not on the market.
Pioneering work by NCASI, the The National Council for Air and Stream Improvement, had pegged the response ratio such that approximately 3 ppm of chlorine is required to cause a 1 ppm reading on an Interscan chlorine dioxide analyzer.
Subsequent efforts have refined the number a bit. We now advise our customers that:
2.8 ppm of chlorine will show a 1 ppm reading on a chlorine dioxide analyzer, and this ratio is stated with an accuracy of ±10%
For our own in-house work, Interscan does generate ClO2, and does not use a surrogate. Many of our customers use our popular SENSOR EXPRESS® program for their ClO2 calibration requirements.