Method and system for sampling and determining the presence of compounds

A system for detecting selected compounds, including certain nitrogen containing compounds in a sample by chemiluminescent gas phase reaction of nitric oxide with ozone, said nitric oxide being present as either a background component in the sample or as a product of the conversion of one of said nitrogen containing compounds comprising:

• means for collecting the sample;
• means for dividing the sample into first and second portions;
• first converter means for heating the first portion of the sample to a first predetermined temperature, said first converter means having first conversion properties such that no appreciable amounts of nitric oxide can be produced therein from the nitrogen containing compounds;
• second converter means for heating the second portion of the sample to a second predetermined temperature, said second converter means having second conversion properties such that measurable amounts of nitric oxide can be produced therein from the nitrogen containing compounds;
• means for mixing the heated first portion of the sample with ozone to cause a chemical reaction therewith in order to generate radiation by chemiluminescence having characteristic wavelengths related to nitric oxide from the background component in said first portion;
• means for mixing the heated second portion of the sample with ozone to cause a chemical reaction therewith in order to generate radiation by chemiluminescence having characteristic wavelengths related to nitric oxide from the background component and also nitric oxide formed from conversion of nitrogen containing compounds in said second portion;
• means for selectively detecting radiation emitted by chemiluminescence from the first portion of the sample;
• means for selectively detecting radiation emitted by chemiluminescence from the second portion of the sample;
• means for generating first electrical signals having amplitudes and durations related to the detected characteristic wavelengths of radiation emitted from the mixed first portion of the sample and second electrical signals having amplitudes and durations related to the detected characteristic wavelengths of radiation emitted from the mixed second portion of the sample;
• and
• means for comparing the first electrical signals with the second electrical signals in order to determine the presence or absence of selected nitrogen containing compounds in the sample;
• said heating, mixing, detecting, and generating means being operable to process said first portion at substantially the same relative times as the processing of said second portion thereby to permit cancellation of signals related to background components of nitric oxide signals from said first and second electrical signals by said comparing means.