The California Analytical 700 Series CLD Analyzer utilizes the principle of chemiluminescence for analyzing the NO or NOx concentration within a gaseous sample. In the NO mode, the method is based upon the chemiluminescent reaction between ozone and nitric oxide (NO) yielding nitrogen dioxide (NO2) and oxygen. This reaction produces light which has intensity proportional to the mass flow rate of NO2 into the reaction chamber. The light is measured by means of a photodiode and associated amplification electronics. In the NOx mode, NO plus NO2 is determined as above, however, the sample is first routed through the internal NO2 to NO converter which converts the NO2 in the sample to NO. The resultant reaction is directly proportional to the total concentration of NOx.