Teledyne T100, Instruction Manual, Page: 223 / 404

Teledyne ML - T100 UV Fluorescence SO2 Analyzer Theory Of Operation
06807A(DCNxxxx) 223
second stage of this reaction occurs after the SO
2
reaches its excited state (SO
2
*).
Because the The system will seek the lowest available stable energy state, the SO
2
*
molecule quickly returns to its ground state (Equation 10-3) by giving off the excess
energy in the form of a photon (
h

). The wavelength of this fluoresced light is also in
the ultraviolet band but at a longer (lower energy) wavelength centered at 330nm.
nm 330 2 2
hv SO * SO     
(Equation 9-3)
The amount of detectable UV given off by the decay of the SO
2
* is affected the rate at
which this reaction occurs ( k ).
 
* SO k F
2

(Equation 9-4)
Where:
F =
the amount of fluorescent light given off.
k
=
The rate at which the SO
2
* decays into SO
2.
SO
2
*
=
Amount of excited SO
2
in the sample chamber.
Therefore:
 
nm 330 2
F
2
hv SO * SO k     
(Equation 9-5)
Finally, the function ( k ) is affected by the temperature of the gas. The warmer the gas,
the faster the individual molecules decay back into their ground state and the more
photons of UV light are given off per unit of time.
In summary, given that the absorption rate of SO
2
( a ) is constant, the amount of
fluorescence ( F ) is a result of:

The amount of exited SO
2
* created which is affected by the variable factors from (Equation
9-2) above: concentration of SO
2
; intensity of UV light ( I
0
); path length of the UV light( x )
and;

The amount of fluorescent light created which is affected by the variable factors from
(Equation 9-5): the amount of SO
2
* present and the rate of decay ( k ) which changes based
on the temperature of the gas.
When and the intensity of the light ( I
0
) is known; path length of excited light is short ( x );
the temperature of the gas is known and compensated for so that the rate of SO
2
*decay
is constant ( k ). and; no interfering conditions are present (such as interfering gases or
stray light); the amount of fluorescent light emitted ( F ) is directly related to the
concentration of the SO
2
in the Sample Chamber.