You may possibly want to check: http://pubs.rsc.org/en/content/articlelanding/1987/an/an9871201743#!divAbstract
my dear,look this link
https://en.wikipedia.org/wiki/Chemical_oxygen_demand
Standard ferrous ammonium sulfate titrant (FAS), approximately 0.10M:
Dissolve 39.2 g Fe (NH4)2(SO4)2.6H2O in distilled water. Add 20 mL conc.
H2SO4, cool, and dilute to 1000 mL. Standardize solution daily against standard K2Cr2O7
digestion solution as follows: Pipet 5.00 mL digestion solution into a small beaker. Add 10 mL
reagent water to substitute for sample. Cool to room temperature. Add 1 to 2 drops diluted
Ferroin indicator and titrate with FAS titrant.
Molarity of FAS solution = [Vol K2Cr2O7 ×0.1] / (Vol FAS)
http://web.iitd.ac.in/~arunku/files/CEL212_Y14/CEL%20212%20Lab%205%20COD%20and%20DO.pdf
The authoritative text on all aspects is published by the American Public Health and Wastewater Association
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