CHEM I CAL OX Y GEN DE MAND
MODEL AB-COD · CODE 7637
QUANTITY CONTENTS CODE
10 g *Mercuric Sulfate Powder *7581-D
230 mL *Potassium Dichromate, 0.25N *7582-K
3 x 230 mL *COD Reagent #3 *7583-K
30 mL *Ferroin Indicator *7584-G
2 x 230 mL *Ferrous Ammonium Sulfate, 0.05N *7585-K
30 mL *Sulfuric Acid, 25% *7588-G
60 mL Potassium Biphthalate Solution 7589-H
2 x 250 mL Deionized Water 5115PS-K
1 Flask, Flat Bottom, 50 mL, glass 0887
1 Condenser, 20 cm, glass 0888
2 Clamps, utility, metal 0396
1 Vial Glass Beads 0889
2 Flasks, Erlenmeyer, 125 mL, glass 0431
1 Graduated Cylinder, 50 mL, glass 0418
2 Graduated Cylinders, 10 mL, glass 0416
1 Spoon, 0.1 g, plastic 0699
1 Latex Tubing, 6 feet 0891-6
1 Automatic Buret 0427
1 Pipet, plain, plastic 0352
1 Pipet Assembly, 20 mm 0341
1 Water Sample Bottle 0688
*WARNING: Reagents marked with an * are considered hazardous substances.
To view or print a Material Safety Data Sheet (MSDS) for these reagents see
MSDS CD or our web site. To obtain a printed copy, contact us by e-mail, phone
or fax.
To order a complete set of refill reagents, order as R-7637. To order individual
reagents or test kit components, use the specified code number.
SAM PLING AND STOR AGE
Samples are taken with clean water sampling bottles which are free of
organic matter. The COD determination should be made almost
immediately after the sample is taken. If, for some reason, the COD
analysis cannot be made immediately, the sample is made acidic (pH 2 pH 3) by adding a few drops of 25% Sulfuric Acid (7588) and stored at
4-8oC. For longer storage periods, deep-freezing is recommended. Samples
containing detritus or settleable solids should be homogenized by a blender
to obtain a representative sample. All dilutions should be made with
deionized water and should be measured accurately in volumetric flasks.
AP PA RA TUS
A hot plate is necessary to provide adequate boiling of the reagents in the
reflux mixture. A metal stand is required to hold both the distilling flask
and the reflux condenser. All the other material required to make a COD
analysis is supplied with the LaMotte Chemical Oxygen Demand Outfit.
STAN DARD IZA TION
*Ferrous Ammonium Sulfate, 0.05N (7585) must be restandardized before
a series of analysis is started, due to its unstable nature. To determine the
normality of *Ferrous Ammonium Sulfate, 0.05N (7585), dilute 5 mL of
*Potassium Dichromate, 0.25N (7582) to 50 mL with Deionized Water
(5115). Add 15 mL *COD Reagent #3 (7583) and allow to cool. Titrate
with *Ferrous Ammonium Sulfate, 0.05N (7585) using 3-5 drops of Ferroin
Indicator (7584) and substitute the values in the following equation:
Normality of Reagent #5 =
mL Potassium Dichromate, 0.25N
mL Ferrous Ammonium Sulfate, 0.05N
x .25
PRO CE DURE
A blank consisting of 10 mL of distilled water must be run with all the
reagents. The blank is refluxed and analyzed in the same manner as
outlined above.
1. Fill graduated cylinder (0416) to 10 mL line with sample water.
Transfer to 50 mL flat bottom flask (0887).
2. Use the 0.1 g spoon (0699) to add 0.2 g *Mercuric Sulfate Powder
(7851). Mix.
3. Use a second graduated cylinder (0416) to add 5 mL of *Potassium
Dichromate, 0.25N (7582). Mix.
4. Fill graduated cylinder (0418) to 15 mL line with *COD Reagent #3
(7583). Add small portions at a time to the distillation flask, mixing
well with each addition.
CAUTION: *COD Reagent #3 (7583) is Sulfuric Acid. Read
Material Safety Data Sheets (MSDS).
5. Add 5-10 glass beads (0889) to the flask.
CAUTION: The reflux mixture should be thoroughly mixed before
heating.
6. Attach the reflux flask to the condenser (0888). Connect the
rubber tubing to the condenser and to the faucet.
NOTE: Be sure that the condenser and reflux flask are held securely
on a hot plate by the clamps and adjust the water flow through the
condenser so that water pressure does not build up within the
condenser.
7. Boil contents of reflux flask for 2 hours.
NOTE: Shorter time periods may be used for some samples which are
low in organic matter if the COD gives the maximum value using the
shorter time periods. Samples containing a high concentration of
organic matter will consume all the dichromate: as a result, no
endpoint can be obtained with the titration. If this is the case, the
untreated sample must be diluted with deionized water until there is
an excess of titratable dichromate. Repeat Steps 1-7 on the diluted
sample and multiply the results by the dilution factor.
8. Wait for mixture to cool. Pour the contents of the reflux flask into the
rinsed 50 mL graduated cylinder (0418). Wash down the insides of the
condenser and the reflux flask with Deionized Water (5115PS) adding
the washing to the sample in the graduated cylinder. Dilute to 50 mL
with Deionized Water (5115PS). Mix. Pour the diluted sample into a
125 mL Erlenmeyer flask (0431).
9. Add drops of *Ferroin Indicator (7584) until the color of the sample is
bluish-green. Usually 3-5 drops of indicator are sufficient.
10. Fill the buret (0427) to the 10 mL mark with *Ferrous Ammonium
Sulfate, 0.05N (7585). While gently swirling the flask, add *Ferrous
Ammonium Sulfate, 0.05N until solution turns reddish-brown.
NOTE: The first color change is the endpoint.
CAL CU LA TION
COD, chemical oxygen demand from dichromate:
mg/L COD =
A = mL *Ferrous Ammonium Sulfate, 0.05N used for blank
B = mL *Ferrous Ammonium Sulfate, 0.05N used for sample
C = Normality of *Ferrous Ammonium Sulfate, 0.05N
(A - B) x C x 8,000
mL sample
STAN DARD SO LU TION
The procedure and reagents can be checked using a standard solution of
potassium biphthalate. Potassium biphthalate yields 98-100% of the
theoretical oxygen demand and also is stable over a period of time. A
Potassium Biphthalate Solution (7589) is furnished in the kit and has a
theoretical oxygen demand of 500 mg/L for a 10 mL sample. Appropriate
dilutions can be made to bring the concentration of potassium biphthalate
within the desired range.
REFERENCES: Standard Methods for the Examination of Water and Waste Water,
16th Edition APHA, AWWA, WPCF, New York, 1985.
LaMOTTE COM PANY
Helping Peo ple Solve An a lyt i cal Chal lenges
PO Box 329 • Chestertown • Mary land • 21620 • USA
800-344-3100 • 410-778-3100 (Out side U.S.A.) • Fax 410-778-6394
Visit us on the web at www.lamotte.com
SM
9/03
Loading...