Measuring method
44 Edition 01/2016 multi EA 4000
3 (CO
3
)
2-
+ 2 H
3
PO
4
3 H
2
O + 3 CO
2
+ 2(PO
4
)
3-
(3)
The sample digestion takes place in a TIC solids module. The measuring gas is detected in
the C/S module.
5.3 TOC analysis
During the TOC analysis the total organic carbon content of a sample is detected.
In the multi EA 4000 the TOC content can be determined in two ways:
Differential method
Direct method
The differential method should be used when the sample contains easily purgeable organic
substances as benzene, cyclohexane, chloroform, etc. The differential method should not be
used when the TIC content of the sample is significantly higher than the TOC content.
IMPORTANT
For the TOC analysis using the automatic solids module the differential method should be
preferred. The combustion tube and detectors are then not loaded with acid.
5.3.1 Differential method for the TOC analysis
The differential method can take place using the automatic TIC solids module. The sample is
weight onto two boats. The TIC and TC are determined in consecutive measurements. The
calculated difference is given as TOC. The differential method detects volatile as well as
non-volatile organic carbon compounds.
TOC = TC – TIC (4)
TOC ... total organic carbon
TC ... total carbon
TIC ... total inorganic carbon
5.3.2 Direct method for the TOC analysis
With the automatic TIC solids module the TIC and TOC can also be detected directly. After
purging the TIC in the TIC reactor with hydrochloric acid and detecting the TIC content, the
sample boat is transferred to the combustion tube. As in the TC/TS analysis, the sample is
dissolved and oxidized in the oxygen flow at high temperature.
For the detection of TOC using the automatic TIC solids module hydrochloric acid has to be
added to the sample. Therefore, the differential method is preferred for
the TOC analysis.
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