LaMotte COD3 Plus, Operator'S Manual

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Dissolved Oxygen
COD3 Plus Colorimeter 10.16
COLLECTION & TREATMENT OF THE WATER SAMPLE
Steps 1 through 4 below describe proper sampling technique in shallow water. For
sample collection at depths beyond arm’s reach, special water sampling apparatus
is required (e.g. the LaMotte Water Sampling Chamber, Code 1060; Model JT-1 Water
Samplers, Code 1077; Water Sampling Outfi t, Code 3103; or Water Sampling Bottle,
Code 3-0026).
1. To avoid contamination, thoroughly rinse the screw cap Sample Tube (29180) with
sample water.
2. Tightly cap Sample Tube and submerge to the desired depth. Remove cap and
allow the Sample Tube to fi ll.
3. Tap the sides of the submerged tube to dislodge any air bubbles clinging to the
inside. Replace the cap while the Sample Tube is still submerged.
4. Retrieve Sample Tube and examine it carefully to make sure that no air bubbles
are trapped inside. Once a satisfactory sample has been collected, proceed
immediately with Steps 5 and 6 to “fi x” the sample.
NOTE: Be careful not to introduce air into the sample while adding the reagents in
steps 5 and 6. Simply drop the reagents into the sample. Cap carefully, and mix
gently.
5. Add 2 drops of *Manganese Sulfate Solution (4167) and 2 drops of *Alkaline
Potassium Iodide Azide (7166). Cap and mix by inverting several times. A
precipitate will form. Allow the precipitate to settle below the shoulder of the tube
before proceeding.
6. Add 8 drops of *Sulfuric Acid, 1:1 (6141WT). Cap and gently mix until the
precipitate has dissolved. A clear-yellow to brown-orange color will develop,
depending on the oxygen content of the sample.
NOTE: It is very important that all “brown fl akes” are dissolved completely. If the
water has a high DO level this could take several minutes. If fl akes are not completely
dissolved after 5 minutes, add 2 drops of *Sulfuric Acid 1:1 (6141WT) and continue
mixing.
NOTE: Following the completion of step 6, contact between the water sample and the
atmosphere will not aff ect the test result. Once the sample has been “fi xed” in this
manner, it is not necessary to perform the actual test procedure immediately. Thus,
several samples can be collected and “fi xed” in the fi eld, and then carried back to a
testing station or laboratory where the test procedure is to be performed.
Testing