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. |
