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Measuring methods
4.3
TOC analysis
4.3.1
Differential method for the TOC analysis
42
To determine the inorganic carbon (TIC), acid is added to an aliquot of the sample.
This leads to the decomposition of the carbonates/hydrogen carbonates contained
therein. The CO
is purged and detected. No thermal oxidation takes place.
2
3 (CO
)
+ 2 H
PO
3 H
2-
3
3
4
The sample digestion takes place in a TIC solids module. The measuring gas is detected
in the C/S module.
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 or-
ganic 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.
NOTICE
For the TOC analysis with the automatic TIC solids module the differential method is
preferred. The combustion tube and detectors are not exposed to acid in this case.
The differential method can take place using the automatic TIC solids module. The
sample is weight in on two boats. Two consecutive measurements are used to deter-
mine TIC and TC. The calculated difference is given as TOC. The differential method
detects volatile as well as non-volatile organic carbon compounds.
TOC = TC – TIC
TOC
total organic carbon
TC
total carbon
TIC
total inorganic carbon
O + 3 CO
+ 2 (PO
)
3-
2
2
4
multi EA 4000
(3)
(4)
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