Teledyne 6750 - Total Organic Carbon analyzers - Manual (Page 19)

Total Organic Carbon Analyzer Theory of Operation
Teledyne Analytical Instruments 7
(sparges) the CO
2
converted from the TIC and it is measured by an
independent CO
2
detector as “TIC”. POC is also stripped from the
sample in the sparger as HC, but the HC is undetected by the CO
2
detector and does not interfere with the TIC measurement.
A portion of the same sample is also directed to the oxidation
reactor, where inorganic and all organic carbon is converted to CO
2
and
detected by a second CO
2
detector as “Total Carbon”.
A mathematical subtraction of the TIC from the TC measurement
yields a complete, Total Organic Carbon analysis performed as a “TOC-
True” method.
TOC - True = TC - TIC
The difference between the Model 6750’s TOC-True Method
and other simple (TC-TIC) subtraction methods is that most other
simple TC-TIC subtraction methods only deal with a TC measurement,
then a separate TIC measurement and a simple mathematical difference
to derive a “TOC” analysis.
In the TOC-True method used by the Model 6750, the analyzer
actually performs both TC and TIC measurements simultaneously and
continuously on the same sample. The TOC Measurement Basics and
Methods are illustrated in Figures 2-3 and 2-4.
In conclusion:
1. NPOC is the preferred method if no POC/VOC is present
in the sample.
2. TOC-True is the preferred method if POC/VOC exists in
the sample and a TOC analysis is desired which includes
all organic carbon species, for a TOTAL Organic Carbon
measurement.