As we can see in the attached manual we have to prepare for every single sample one TC and one TIC cuvette.
Both of them have to be measured as given in the manual.
The TOC will be only calculated by the subtraction of measuring result TIC from measuring result TC: TC-TIC= TOC
If we use a DR-instrument we have to measure both cuvettes first TC than TIC and after that we will get the final result.
(Please see and follow procedure given on page 5)
So, if we have mixed up the cuvettes we may get some negative results.