Lamotte P-6741-H DPD 1B Free Chlorine Reagent 60 mL. The liquid alternative to DPD tablets can be used with existing LaMotte chlorine comparators or colorimeters. DPD 1A and DPD 1B are added to a 5 or 10 mL sample to test Free Available Chlorine. DPD 3 is added to the reacted sample to measure Total Chlorine. Also, liquid reagents are available to measure pH, Hardness, Alkalinity, Copper, and other liquid reagents.