c. Blank determination:
i. Place approximately 15 mL Milli-Q water in a BOD bottle with a stir
bar. Add 1 mL of the potassium iodate standard, mix thoroughly, then
add 1 mL 50% sulfuric acid, again mixing the solution thoroughly.
ii. Before beginning the titration, add the following reagents: 1 mL sodium
iodide-sodium hydroxide reagent (#1), rinse, mix, then add 1 mL
manganese chloride reagent (#2). Fill the BOD bottle to just below the
neck with Milli-Q water. Titrate to the endpoint as described for the
sample analysis procedure (below).
iii. Pipet 1 mL of the standard solution into the same flask and again titrate
to the end point.
iv. The difference between the first and second titration is the reagent blank.
Either positive or negative blanks are possible.