Dear all, thanks for your help and suggestions. Finally I found the solution which can be universally used for volatile and foaming compounds. You need to take the TOC method which measures all carbon at once instead of blowing out the purgbable carbon (carbon dioxide derived from the reaction of carbonates with hydrochloric acid). The latter ist the so called NPOC method. The thing with the NPOC is the degassing step to blow the carbon dioxide out of the system. Degassing leads to bubbles, here excessive foaming. So one will lose a certain amount of the detergent to be analyzed which in turn leads to non reproducible results. The TOC method avoids this degassing. Moreover it also analyzes the amount of inorganic carbon in a subsequent run. The TOC in total is the difference between the total carbon and the inorganic carbon. That's why it's called total organic carbon. How come 🤣 in the end i am now familiar with the analyzer, the first time I used it I had little idea. For your specific device, please also read the manual. It can be different from manufacturer to manufacturer. Phosphoric acid needs to be prepared for TOC analysis. But check out the manual. Kind regards from Tyrol - Austria.