w/ 0.5 mL 1:1 Sulfuric Acid for Nitrate/Nitrite; COD Oil and Grease and TPH testing. Pack of 12 EP preserved containers EP Preserved Containers™ simplify field preservation. Level 1 Products include a certificate of analysis for the container and the added reagent. (Level 1 certified containers recieve full EPA quality assurance; each case is custody sealed and each container is lot numbered for tracibility) EP Preserved™ containers provide an extra measure of assurance that proper sampling protocols are followed especially when collecting for a number of parameters