GE Analytical Instruments ©2016
58 of 270
DLM 68100-09 EN Rev. A
Chapter 2: System Description
The solution is not sparged when TC, IC, or TOC (TC-IC) is measured. However, IC is lost from the solution while it is
in the sparging chamber because the solution is acidic, and the IC is converted into volatile CO
2
. The instrument
calibration procedures include a method of calibrating the IC measurement, which should be used whenever
the samples are expected to contain significant concentrations of IC, and NPOC will
not
be measured.
Next, solution is pumped from the sparger by the peristaltic pump in the Reactor Module into the reactor tube,
which is at room temperature. The high-pressure valves at each end of the reactor tube seal it. When NPOC or
TC is to be measured, the reactor is rapidly heated to 375 °C (707 °F)
2
and supercritical water oxidation (SCWO)
of the organics is completed within 3 min.
When water is heated to 375°C
2
in a sealed reactor, the pressure rises to more than 3,200 psi (22.1 MPa), which
is above the critical point of water. Supercritical water is a fluid that has special properties that are very
beneficial for TOC measurement:
•
Supercritical water is nonpolar, so organics that are not highly soluble in water become very soluble.
Oxygen, produced by the decomposition of the persulfate anion, becomes very soluble. However, salts
that normally dissolve in water are not soluble in supercritical water.
•
Supercritical water has a very low viscosity and a high diffusibility. Therefore, the oxidation is fast
because of the rapid transport of reactants.
The benefits of SCWO are perhaps most pronounced when the sample contains high concentrations of chloride.
Traditional TOC measurement techniques, involving oxidation with persulfate, are inefficient with those samples
because much of the oxidizing power of the persulfate is consumed by the oxidation of the chloride. However,
the InnovOx TOC Analyzer can oxidize chloride-containing samples without excessive formation of chlorine
because the salt is not soluble during the oxidation process.
Additionally, hard-to-oxidize organics that would not be oxidized by persulfate at normal temperatures, even
when the oxidation is initiated by UV radiation, are virtually completely oxidized in the InnovOx TOC Analyzer.
This is partly because organics, which normally are not soluble (such as cellulose), are soluble in supercritical
water.
The Reactor Module is designed to have a low thermal mass, allowing the reactor tube to be heated rapidly, and
then cooled rapidly. When the oxidation period is completed, the reactor is cooled by turning off the heater and
blowing ambient air over the reactor tube. Within about 110 seconds, the reactor is nearly room temperature.
The high-pressure valves are opened, and the CO
2
in the reactor is flushed out by the carrier gas. Salts dissolve
again in the water as it cools, and are flushed out of the reactor, along with any particulates remaining the
solution.
2.
The reactor temperature of 375° C should not be confused with the heater testing criteria temperature used
in diagnostics (355° ±5° temperature), as the testing criteria temperature in the diagnostics process is an
indirect measurement of a controlled reactor temperature. The control point (used in diagnostics) has been
demonstrated to achieve a reactor temperature of 375° C necessary to create supercritical water in the
Analyzer’s sample flow path. For additional information on the heater testing criteria see
