Methods
Dissolved Oxygen: Instructions for the use of LaMotte Kits
Fixing the Sample
1) After putting on gloves and safety glasses, carefully add 8 drops of the Manganous Sulfate
Solution without touching the reagent bottle to the sample.
2) Similarly, add 8 drops of Alkaline Potassium Iodide Azide. Recap the bottle and mix the
contents by inverting the bottle several times. A pale precipitate will form.
3) Allow the precipitate to settle to below the shoulder of the bottle, about one-third
to one-half way to the bottom of the bottle.
4) Carefully open the bottle and add acid to dissolve the precipitate.
4a) If provided with liquid sulfuric acid, add 8 drops without touching the bottle to the sample.
4b) If provided with sulfamic powder add one level measure (about 1 gram) using
the plastic scoop provided. Be very cautious of any wind that could blow the acid powder.
5) Recap the bottle and gently mix the contents by inverting the bottle several times.
At this point all of the precipitate should dissolve, and if oxygen is present the solution
will turn golden yellow. The sample is now fixed and can be analyzed later.
Analysis of the Sample
1) Wearing gloves and safety glasses, open the sample bottle and fill the titration tube
to the 20 ml line.
Water in the tube will form a meniscus; a concave curved surface that is higher around the
edges and lower in the center. The tube should be filled so that the bottom of the meniscus
is level with the 20ml graduation line. Cap the tube.
2) Making sure the plunger on the titrator is completely depressed, insert the titrator
into the bottle of Sodium Thiosulfate. Invert the bottle and titrator, and slowly withdraw
the plunger until the indicator on the plunger is opposite the zero mark. If air bubbles are
present in the titrator, completely depress the plunger and refill the titrator. Once the
titrator is full and free of air bubbles, turn the bottle upright and remove the titrator.
3) Insert the tip of the Titrator into the cap on the titration tube. Slowly depress the
plunger, adding thiosulfate to the sample one drop at a time.
Continue adding thiosulfate until the solution turns pale yellow. Be sure to swirl the tube
in between adding drops of thiosulfate.
4) Remove the titrator and uncap the tube. Add 8 drops of starch indicator. The solution
should turn a deep blue color which aids in seeing the color change.
5) Recap the tube and replace the titrator. Add thiosulfate one drop at a time until the
solution turns from blue to colorless. Be sure to swirl the tube between drops. If you
deplete the thiosulfate, refer to step 3 to refill the titrator completely.
6) Now read the scale on the titrator. Each line represents 0.2 ppm. If you had to refill
the titrator, remember to add 10 ppm to your final result.
Back to Sample Collecting and Fixing
Instructions for the use of Hach Kits
Back to main DO page