Dosimeter for oxides of nitrogen

A simple, lightweight, prototype dosimeter, based on wet chemical principles, has been developed for personal monitoring of NO2. A simple modification provides for the determination of NOx. This device requires no auxiliary equipment and is intrinsically safe for use in coal mines. In use, NO2 permeates a membrane and is absorbed in acidic aqueous solution containing hydrogen peroxide. The latter oxidizes NO2 to nitrate. When a total NOx determination is required, an oxidizing prefilter converts NO to NO2 prior to conversion to nitrate in solution. The NO3--is determined in the laboratory with a specific ion electrode. The NO2 or NOx is determined from the NO3--found with reasonably good precision and accuracy. Caution should be exercised when using a dosimeter to determine compounds having a "C" value. These devices will not indicate an excursion concentration existing during a limited time. Effects due to dosimeter orientation, liquid evaporation, and temperature (above 15 degrees) were insignificant. Prior to field testing, it would be desirable to conduct more extensive laboratory tests. The entire TLV range of NO (up to 25 ppm) should be covered, and exposure of the dosimeters to known mixtures of NO and NO2 should be evaluated. Tests against specific interferences should also be performed.