Ionics Instruments 2004 Page 3-6 DLM 30007-08 Rev. A
Oxidation Reactor
The analyzer oxidizes organic compounds to CO
2
using the chemical oxidizing
agent ammonium persulfate, and UV radiation. The oxidation reactor is a
spiral quartz tube wrapped around an UV lamp. The lamp emits light at 184
and 254 nanometers, resulting in the formation of powerful chemical oxidizing
agents from the photolysis of water and persulfate:
H
2
O + hn (184 nm) OH
.
+ H
.
(1)
S
2
O
8
-
2
+ hn (254 nm) 2 SO
4
.-
(2)
SO
4
.-
+ H
2
O HSO
4
-
+ OH
.
(3)
Hydroxyl radical (OH
.
) will completely oxidize organic compounds to form
carbon dioxide:
Organic Compounds + OH
.
CO
2
+ H
2
O (4)
When low levels of organic compounds (< 1 ppm) are present in the sample,
complete oxidation can usually be achieved by hydroxyl radicals produced
from the photolysis of water, without the addition of persulfate.
The lifetime of the UV lamp is approximately 6 months of operation and a
warning message will indicate when it is time to replace the lamp.
CO
2
Sensors
Two membrane-based conductometric CO
2
sensors, a TC and an IC, are used
in the analyzer. One DI water source serves both sensors and each CO
2
sensor consists of a membrane module, and a conductivity and temperature
measurement cell. The IC sensor measures the concentration of CO
2
in the
sample (without oxidation). The TC sensor measures the combined
concentration of CO
2
initially in the sample and CO
2
produced by the oxidation
of organic compounds.
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