Why does the Hach CBOD procedure use a different amount of nitrification inhibitor than Standard Methods?

Document ID

Document ID TE171

Published Date

Published Date 27/05/2017
Question
Why does the Hach CBOD procedure use a different amount of nitrification inhibitor than Standard Methods?
Summary
Amount of Nitrification Inhibitor for CBOD
Answer
Previous versions of Standard Methods have referenced varying amounts of TCMP but the actual amount in the sample is the same: 3 mg.  The Hach dilution method 8043 calls for the use of Nitrification inhibitor catalog number 253335.  The Hach nitrification inhibitor contains 2% TCMP; adding 0.160 g of this introduces 3 mg (0.160 *0.02) of TCMP, the same amount as that called for in SM 5210.