GLOBE Hydrology Protocol

Testing for the presence of Disssolved Oxygen

in surface water samples

The chemical analysis of water samples is a bit more complicated than some elementary students can understand; so instead of teaching chemical names and processes, this presentation is aimed at teaching the physical changes that a sample undergoes as it is examined.

For this reason, chemical names have been replaced by colors for each solution bottle cap. Instead of titration, students are expected to observe color changes and read measurements off the syringe. Thus the procedures for conducting dissolved oxygen tests is simplified to the basic steps illustrated below:

Step A - Collect and Fix the sample (to be accomplished at the stream or pond site)

Rinse the sample bottle in source water.

Submerge sample bottle and fill with water.

Insure no air is trapped inside bottle when cap is replaced.

Open sample bottle and add eight (8) drops of red cap solution and replace the red cap.

Add eight (8) drops of blue cap solution and replace the blue cap. Watch for a milky substance to form in the sample bottle. Cap and shake the bottle. Allow precipitate to settle before the next step.

Add one (1) scoop of powder and place black cap back on the sample bottle. Shake well (until solution is clear yellow with no brown flakes).

Solution is now FIXED so oxygen level won't change any more. Further testing can be done later.

Step B - Measuring the Dissolved Oxygen Level (can be done back at the school)

Pour some of the fixed sample into the test bottle with the hole in the cap. Fill to the white line. Cap the test bottle.

Fill syringe up to the -0- line with the solution from the black capped bottle. See the illustration on how to read the syringe. Put the syringe into the hole in the test bottle cap without pushing the plunger.

Add one drop at a time from the syringe and gently swirl the test bottle. Continue until solution is a pale yellow color. (Refill syringe if necessary.)

Open test bottle and add eight (8) drops of the green cap solution and replace the green cap. Swirl the test bottle. The test bottle solution turns a black or dark purple color.

Replace syringe and cap and continue adding one drop at a time and swirling until the test bottle solution turns clear. If a re-fill of solution is needed, fill the entire syringe again. Once the test bottle turns colorless, Stop. Read the markings on the syringe (and add 10 if another syringe was needed).

The readings from the syringe equals the Dissolved Oxygen level in parts per million (ppm) or milligrams / Liter (mg/L). Record the reading.

Step C - Checking the Testing Solutions to see if they are still good. This is really beyond the understanding of young students so it is best done by the teacher or a knowledgable parent. None of the reageants nor hardware was included in the GLOBE equipment issue. As a minimum, the following items must be purchased for this calibration titration:

Item - - - - - - - - - - - - Lamotte code #

Titration tube 15ml - - (0299) (you may use a small graduate cylinder and the titration bottle in the DO kit)

Titrator, 0-1 range - - - (0376)

Sulfuric Acid, 5N - - - (8517WT) (Material is corrosive and toxic - student use must be supervised)

Spoon, 0.1 gram - - - - (0699)

Potassium Iodide - - - -(6809)

>Should the 0.025N Sodium Thiosulfate Test Solution be out of date (over shelf life) and test outside the range specified, discard in accordance with manufacturer's instructions and replace with fresh test solution.