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Chapter 3: Interferences
Reliability
The reliability of the Analyzer can be affected by other interferences. Some interferences corrode the titanium
reactor tube, reactor valves, or other Analyzer components. Samples containing the following should be
avoided:
•
Hydrofluoric acid
•
Fluoride
•
Concentrated reducing acids, including HCl, HBr, HI, H
Other interferences form precipitates when acidified or oxidized. Thiosulfate precipitates sulfur when acidified.
The precipitate may plug the Sparger, tubing in various places in the Analyzer, and Reactor.
Some precipitates may be avoided by proper selection of the acid. To determine if the sample is likely to form
precipitates, take a volume of the sample and add about 1% (by volume) acid to it. If a precipitate forms when
6 M H
PO
is used, try 3 M HCl. Next, add about 15% (by volume) of the oxidizer solution to the sample. This will
3
4
indicate if precipitate would form when the sample is mixed with the oxidizer.
Samples that contain excessively high levels of volatile organic compounds (VOCs) may require accelerated
preventative maintenance of the sample tubing.
The Analyzer should be used in a well-ventilated workspace. Corrosive gases or vapors that are allowed to come
in contact with the Analyzer will promote corrosion of certain components.
When the Analyzer runs highly acidic or caustic samples via the vial port or side sample port, it is recommended
to run a vial of blank water at the end of the protocol. This helps rinse the sample flow path and extends the life
of the Analyzer.
Analytical Performance
If the sample contains inorganic reducing compounds, those compounds often consume some of the oxidizer,
causing incomplete oxidation of organic compounds. The result is low NPOC, TC, and TOC measurements.
Species that are known to produce this effect are:
-
-
•
Halides (Cl
, Br
-
•
Nitrite (NO
)
2
This is much less of a problem in the InnovOx TOC Analyzers than in other wet chemical analyzers because the
InnovOx TOC Analyzer uses supercritical water oxidation (SCWO). Salts tend to precipitate in the Reactor when
supercritical conditions are reached. This makes those species less reactive during the oxidation, while the
organic compounds are more soluble and, therefore, more reactive.
GE Analytical Instruments ©2016
-
, and I
)
SO
, or H
PO
2
4
3
68 of 270
4
DLM 68100-09 EN Rev. A
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