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A Close Look at the Specialists: TOC and TNb in Every Matrix Bernd Bletzinger, Product Specialist, Analytik Jena AG, Konrad-Zuse-Str. 1, 07745 Jena, info@analytik-jena.com


For several decades, the TOC parameter has stand for the total of all organic contaminants in water samples, soils, sediments and construction rubble. Since it is often impossible or simply unnecessary to record the many possible organic compounds separately in a single substance analysis, the TOC sum parameter provides a quick and cost saving alternative for recording a sample's total organic contamination. For this purpose the TOC sum parameter uses the common property of all organic compounds – carbon atoms represent an integral part of every organic compound and can be quantitatively converted into carbon dioxide under defined oxidation conditions and selectively detected. This is done either according to the principle of catalytic high temperature combustion in the oxygen flow or via wet chemical UV oxidation with the help of oxidation agents. Optional solids modules also enable through a robust catalytic-free high temperature combustion the combination of solid and liquid TOC in one device.


The TOC has successfully made its way into a number of application fields. In the field of environment analytics, ground, drinking, surface water (river, lake and sea water) and waste water as well as waste and soil eluates are analysed. But also in several industries, the TOC is used as a process control parameter. In the field of power plants, for example, TOC monitoring is vital in the controlling of the corrosion effects of boiler feed water and cooling water circuits. In pharmaceutical industry, TOC threshold values are established for ultrapure water, water for injection purposes (WFI) and for cleaning process control in pharmaceutical manufacturing (cleaning validation). On top, it is indispensable in the chemical and electroplating industry for the contamination control of acids, base, salts and brines where the ruggedness of the instrument technology is of special interest.


What is the difference between common TOC analysers? Are all devices suitable for this wide range of application fields?


Beside price and quality of the equipment components, the biggest differences consist in the area of sample feed to the reactors as well as in digestion and detection technology. However, it is important to choose the right solution because the differences in these details are crucial. If you want a tailor-made TOC analyser for the specific application, you need a specialist in his field.


The variety of application and benefits of the TOC and TNb sum parameters as well as the applied analyser technology are shown by the selected examples below.


Waste water and solids using the suspension method


The standard DIN EN 15936 ‘Sludge, treated biowaste, soil and waste – Determination of total organic carbon (TOC) by dry combustion’ published in November 2012 with the suspension method contained in informative annex C bring new challenges for liquid TOC analysers.


Both sample matrices have in common that they are solids suspensions with sometimes high contents of particles. DIN EN 1484 defines the TOC as being the sum of dissolved and particle- bound organic compounds. Thus, in the case of TOC analysis it is of special importance to transfer the sample with its solid contents into the reactor in a representative way.


In addition to an effective sample homogenisation on the sample tray of the autosampler, this notably requires a sample introduction technique where particles neither "get lost" on the way nor do very large particles lead to system failure due to blockage or increased wear is to be expected.


In the case of multi N/C® analysers, this is ensured by standard large inner diameters of the


sample introducing components as well as by specific rinsing techniques. The principle of direct injection in the case of multi N/C®


2100 especially convinces by its short sample paths without


any hoses and valve technology. The wastewater specialist realises the most direct transfer of the sample into the combustion system in combination with a septum-free pneumatic furnace head.


The following original measurement table shows the TOC/TNb results as they occur each day in municipal treatment plants at the measurement of inflows and outflows. Special emphasis was


put on the particle handling capacity of the measuring device as well as the recovery of the many included control standards.


TOC in the field of power plants


The challenge consists in the formation of corrosive organic acids and carbonic acid in the boiler feed water out of organic compounds, which are easily oxidised under high pressure and high temperature. TOC monitoring in the boiler feed water is crucial for controlling this process. This is a matter of trace contamination in the range below 1 ppm. Salts are often added as oxygen scavengers.


Table 1. Display of the measured NPOC/TNb values after triplicate determination with the corresponding relative standard deviation


INTERNATIONAL LABMATE - MARCH 2013


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