LaMotte P-6741-G DPD 1B Free Chlorine Liquid Reagent 30 mL 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.