Sum parameters such as Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC) play an important role in water analysis. Both have the potential to replace the Chemical Oxygen Demand (CSB) as a legal limit for wastewater emissions. Pro aqua Diamantelektroden Produktion GmbH developed a new type of device for on-site measurements of TOC/DOC based on electrolysis. However, a suitable sample preparation is needed. The development and optimisation is the main task of this thesis. In the theoretical part, the most important sum parameters for water analysis were defined. Moreover the occurrence, the components and the environmental relevance of organic carbon in water were discussed. Additionally, the legal aspects, especially those concerning limit values and normative standards were discussed. Furthermore, the different methods to determine organic carbons were described and the already existing possibilities to prepare samples, to digest inorganic carbon and to detect carbon dioxide were compared (rapid tests included). The comparison of TOC and CSB, a market study and a description of the new TOC-analyser complete the theoretical part. In the practical part, a buffer system from pH 1.2 to 1.8 was specified. For this purpose, dipotassium phosphate and disodium phosphate as well as potassium dihydrogen phosphate and sodium dihydrogen phosphate monohydrate in combination with phosphoric acid were used. The characteristics of the buffer solutions (production, buffer effect, time dependence of the buffer effect, influences of water hardness, strength of the expulsion of the total inorganic carbon by the buffer, the ideal ratio of sample and buffer, highest possible phosphate input etc.) were collected by experimental approaches. The thesis concludes with comparative measurements with the chair’s own TOC-analyser (stand unit) in comparison to the on-site analyser of Pro aqua Diamantelektroden Produktion GmbH.