LaMotte AG-103 Fresh Water Aquarium - Manual (Page 10)

“FIXING” THE WA TER SAM PLE
NOTE:
Be careful not to introduce air into the sample while adding the
reagents in Steps 5 and 6. Drop the reagents into the test sample, cap
carefully, and mix gently.
5.
Add 8 drops of *Manganous Sulfate Solution (4167) and 8 drops of
*Alkaline Potassium Iodide Azide Solution (7166). Cap and mix by
inverting gently several times. A precipitate will form. Allow the precipitate
to settle below the shoulder of the bottle before proceeding.
6. Use the 1.0g spoon (0697) to add one level measure of *Sulfamic Acid
Powder (6286). Cap and gently invert to mix, until both 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:
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.
TEST PRO CE DURE
1.
Fill the test tube (0608) to the 20 mL line with the “fixed” sample. Cap.
NOTE:
If the color of the “fixed” sample is already a very faint yellow,
skip Step 3, perform Step 4, and begin the titration at Step 5.
2. Fill the Direct Reading Titrator (0377) with *Sodium Thiosulfate
Solution (4169). Insert into the center hole of the test tube cap.
3. While gently shaking the tube, slowly press the plunger to titrate until
the yellow-brown color is reduced to a very faint yellow.
4. Remove the Titrator and cap. Be careful not to disturb the Titrator
plunger, as the titration begun in Step 3 will be continued in Step 5.
Add 8 drops of Starch Indicator Solution (4170WT). Solution will turn
blue.
5. Replace the cap and Titrator and continue titrating until the blue color
just disappears. Read result where plunger meets Titrator Scale. Record
as ppm Dissolved Oxygen. Each minor division equals 0.2 ppm.
6. If the plunger reaches the bottom line on the Titrator scale (10 ppm)
before the endpoint color change occurs, refill the Titrator and continue
the titration. When recording the test result, be sure to include the value
of the original amount of reagent dispensed (10 ppm).
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