Teledyne 6200T - Sulfides Analyzer - Manual (Page 286)

Principles of Operation Model 6200T Total Sulfur Analyzer
286 Teledyne Analytical Instruments
The amount SO
2
converted to excited SO
2
* in the sample chamber is dependent on the
average intensity of the UV light (Ia) and not its peak intensity because the intensity of
UV light is not constant in every part of the sample chamber. Some of the photons are
absorbed by the SO
2
as the light travels through the sample gas.
Darkened
REACTION CELL
filled with SO
2
214nm
Filter UV
SOURCE
Figure 13-1: UV Absorption
The equation for defining the average intensity of the UV light (Ia) is:
     
2 0
SO ax exp 1 I Ia
  
(Equation 13-2)
Where:
I
0
= Intensity of the excitation UV light.
a = The absorption coefficient of SO
2
(a constant).
SO
2
= Concentration of SO
2
in the sample chamber.
x = The distance between the UV source and the SO
2
molecule(s) being affected
(path length).
second stage of this reaction occurs after the SO
2
reaches its excited state (SO
2
*).
Because 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 13-3)