The difference come from dose of chlorine and reaction time. In some standards (German) there is also a difference in that the formation potential is made at standardized pH while the " Simulated Distribution System Trihalomethanes" is made at the natural pH of the sample.

Thanks a lot, dear. One more question, can I use both experiments to study the removal efficiency of disinfection byproduct precursors?

@Henrik Rasmus Andersen

This would depend on your purpose. If you are interested in the potential production of DBPs in the primary or secondary disinfection at the water works you should use the the standard assay and if you are targeting the problem of post disinfection formation of DBPs in the pipes use "Simulated Distribution System Trihalomethanes". I think in most cases the former is most relevant for treatment investigations.

Henrik Rasmus Andersen I appreciate your fast response and valuable information.

Hello Henrik Rasmus Andersen, I've encountered an unexpected result in the lab and I would like to know if you have ever seen this before. My THMFP based on standard method is 68 ug/L (T=25C, pH=7, 7 days, Cl2 residual 3-5 mg/L). However, when I perform the SDS test at T=35 C, the THM SDS goes up to 104ug/L, which is much higher than the THM formation potential. What could be the reason for this? Thank you for your ideas in advance.