The DPD test is commonly used for determination of:

The DPD test, which stands for N,N-diethyl-p-phenylenediamine, is primarily utilized in water quality testing to determine the concentration of chlorine and bromine. This method is based on a colorimetric reaction where the DPD reagent reacts with free chlorine or total chlorine present in water, leading to a color change that can be measured spectrophotometrically.

Chlorine and bromine are both halogens used widely in water disinfection processes. The DPD method is especially favored because it can provide accurate and quick results, allowing water quality professionals to monitor and adjust disinfection levels effectively for safe drinking water and swimming pools.

The other options provided do not utilize the DPD reagent for their detection. Ozone testing is typically performed using different methods, such as ultraviolet absorption or electrochemical sensors. Quaternary ammonium compounds require specific tests, such as those involving colorimetric or titrimetric analysis specifically geared towards those compounds. Iodine is measured using methods like titration with thiosulfate or colorimetric methods but not the DPD method. Therefore, the DPD test is specifically associated with the measurement of chlorine and bromine in various water systems.