ASTM-D1252:06(R2020) pdf free download – Standard Test Methods for Chemical Oxygen Demand (Dichromate Oxygen Demand) of Water.
13. Apparatus
13.1 Rflux Apparatus—The apparatus consists of a 500-mL Erlenmeyer or a 300-mL round-bottom flask, made of heat- resistant glass connected to a 300-mm (12-in.) Any condenser by means of a ground-glass joint. Any equivalent reflux apparatus may be substituted, provided that a ground-glass connection is used between the flask and the condenser, and provided that the flask is made of heat-resistant glass.
1 3.2 Sample Heating Apparatus—A heating mantle or hot plate capable of delivering suflicient controlled heat to main- Lain a steady reflux rate in the reflux apparatus is satisfactory.
1 3.3 Apparatus frr Blending or Homogenizing Samples—A household blender is satisfactory.
14. Reagents
14.1 Ferrous Aminonium Sulfate Solution (0.25 N)— Dissolve 98.0 g of ferrous ammonium sulfate solution (FeSO4•(NH4)SO46H,O) in water. Add 20 mL of sulfuric acid (H2S04. sp gr 1.84), cool and dilute to I L. Standardize this solution daily before use. To standardize, dilute 25.0 mL of 0.25 N potassium dichromate solution (K,Cr,07) to about 250 mL. Add 20 mL of sulfuric acid (sp gr 1.84) and allow the solution to cool. Titrate with the ferrous ammonium sulfate solution to be standardized, using the phenanthroline ferrous sulfate indicator as directed in 15.10. Calculate the normality as follows:
14.2 Ferrous A,nmoniuin Sulfate Solution (0.025 N)— Dilute 100 mL of 0.25 N ferrous ammoniuin sulfate solution to I L. Standardize against 0.025 N potassium dichromate solution as in 14.1. This solution is required only if COD is determined in the range of 10 to 50 mg/L.
14.3 Mercuric Su/fate—Powdered mercuric sulfate (HgSO4).
14.4 Phenan iii roline ferrous Sulfate Indicator Solution— Dissolve 1.48 g of I,10-(ortho)-phenanthroline monohydrate, together with 0.70 g of ferrous sulfate (FeSO47H,O), in 100 mI of water. This indicator may he purchased already prepared.
15.1 Homogenize the sample by blending if necessary. Place 50.0 rnL of the sample in a reflux flask. If less than 50 mL of the sample is used, make up the difference in water, then add the sample aliquot and mix. Samples containing more than 80() mg/L COD are diluted and mixed precisely with water and 50.0 mL of the diluted sample are placed in a reflux flask.
Note I —If the sample is diluted, it must consume at least 5 rnL of dichromatc. Dilute the sample if more than 20 mL of the titrant is needed to reach the endpoint.
15.2 Place 50 mL of water in a reflux flask for the blank de IC tin i nat ion.
15.3 Place the refiux flasks in an ice bath and add I g of powdered mercuric sulfate, 5.0 rnL of concentrated sulfuric acid, and several glass beads or boiling stones. Mix well to complete dissolution.
15.4 With the flasks still in the ice bath, add slowly and with stirring, 25.0 mL of 0.25 N standard potassium dichromate solution.
15.5 With the flasks still in the ice bath, add 70 mL of sulfuric acid-silver sulfate solution slowly such that the solution temperature is maintained as low as possible. preferably below 40°C.