Chemiluminescence is defined as the emission of ultraviolet, visible, or near-infrared radiation through the chemical excitation of a reacting species. In most cases of chemiluminescence, a chemical reaction results in an excited product that emits radiation upon relaxation to its ground electronic state. In general form, chemiluminescence reactions can be expressed as follows:

A + B ----------- C* + D

C* ----------- C + hv

Gas phase chemilumininescent reactions have been observed for over a century since Salet first observed the blue emission from sulfur compounds burned in a hydrogen flame. In the past twenty-five years, chemiluminescence has been extensively used in analytical instrumentation.

Two very desirable features of detectors for the emitted light are high sensitivity and high selectivity toward a particular class of compounds. A detector having these two desirable features for detection of nitrogen compounds is the nitrogen chemiluminescence detector (NCD) based on the chemiluminescent reaction of ozone with NO or other unknown species produced by the oxidative and reductive reactions inside the electrical furnace. A detector having these two desirable features for detection of sulfur compounds is the sulfur chemiluminescence detector (SCD) based on the chemiluminescent reaction of ozone with SO, H2S, or other unknown species produced by the oxidative and reductive reactions inside the electrical furnace.

Many C.I. Analytics instruments utilize state-of-the-art NCD's and SCD's to provide superior analysis of nitrogen and sulfur by chemiluminescence.