LaMotte COD Plus Colorimeter 1922-EX2 - Manual (Page 87)

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 Outfit, 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 fill.
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 “fix” 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 reagent and the precipitate have 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 flakes” are dissolved
completely. If the water has a high DO level this could take several
minutes. If flakes are not completely dissolved after 5 minutes, add 2 drops
of *Sulfuric Acid 1:1 (6141WT) and continue mixing.
Following the completion of step 6, contact between the water sample and the
atmosphere will not affect the test result. Once the sample has been “fixed” in
this manner, it is not necessary to perform the actual test procedure
immediately. Thus, several samples can be collected and “fixed” in the field, and
then carried back to a testing station or laboratory where the test procedure is to
be performed.
DISSOLVED OXYGEN 2/3 COD PLUS TEST PROCEDURES 6/02