The COD reagent also contains silver and mercury ions. Silver is a catalyst, and mercury is used to complex chloride interferences. The measurement wavelength is 348 nm. Consumables and replacement items Required reagents Description Quantity/Test Unit Item no. COD TNTplus ™ Reagent Set, ULR, 1 to 60 mg/L COD 1-2 vials 25/pkg TNT820 Required