Page 9 - 1_Environmental analysis
P. 9

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.
   4   5   6   7   8   9   10   11   12   13   14