Page 10 - Application Handbook - TOC
P. 10
Sum parameter – Total Organic Carbon
TOC – Determination in seawater
SCA-130-104
TOC is an important indicator of the degree of ■ Are high salt loads a problem?
organic contamination. TOC determination is During thermal catalytic combustion of the
used extensively to detect and study test sample, the dissolved salts crystallize.
environmental and seawater pollution. In Depending on the salt concentration, this can
recent years, increased attention is being affect or clog the system. Maintenance
paid to the measurement of the nitrogen measures (for instance exchanging the
compounds (TN = Total Nitrogen) responsible catalyst) would then be required in order to
for eutrophication. render the instrument operational again. Of
course, it is desirable to keep the
maintenance intervals as long as possible.
■ TOC-L Series
The TOC-L series offers various possibilities
to keep the maintenance need for highly
polluted samples as low as possible. The
analyzers are operated under catalytic
combustion at 680 °C. This temperature is
lower than the melting point of sodium
chloride and therefore prevents deactivation
of the active centers of the catalyst by a melt.
■ Seawater samples The use of the platinum catalyst ensures
Seawater has an average salinity of 3.5% complete conversion of organic carbon
mass fraction. The total salinity fluctuates compounds to CO 2.
depending on each ocean. The Baltic Sea The highly sensitive NDIR detector allows
has a salinity of 0.2 to 2%. Some inland seas small injection volumes (typically 20 - 50 µL)
without outlets have far higher water that reduce absolute sample input onto the
salinities. The Dead Sea is known for its catalyst.
salinity of 28%. Chloride ions constitute the
main component of the anions, followed by
sulfate ions. Sodium ions dominate among
the cations, which is why the major proportion
of crystallized sea salts consists of sodium
chloride (common salt). Magnesium, calcium
and potassium ions are represented in
smaller amounts.
