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Water Quality Index Research Methodologies: Dissolved Oxygen
[Dissolved Oxygen Background]

Dissolved oxygen levels can be determined using a variety of tests. AccuVac checks, electronic monitoring, and drop titration are just a few of the methods available. Most tests involve a colormetric change.

Listed below are the instructions for using the Hach Company's OX-2P model 1469-00. It uses the Winkler drop titration method for determining DO amounts.

  1. Remove the stopper and rinse the dissolved oxygen (DO) sample bottle (round, 60ml glass bottle with stopper) with water to be sampled. Empty the bottle.
  2. Immerse the DO bottle beneath the river's surface away from the shore. Use gloves to avoid contact with the river.
  3. Tilt the bottle upstream to fill and allow the water to overflow for two to three minutes. (This will make sure air from the bottle will not be mixed with the stream water.)
  4. Stopper the bottle quickly making sure that you DO NOT TRAP ANY AIR BUBBLES. (The best way to do this is to place the sample bottle on a level, flat surface and then carefully drop the stopper into place.)
  5. Use the clippers to open one Dissolved Oxygen 1 reagent silver foil packet and one Dissolved Oxygen 2 reagent white foil packet. Remove the stopper. Add the contents of each of the packets to the water sample.
  6. Stopper the bottle carefully. MAKE SURE THERE ARE NO AIR BUBBLES. Grip the bottle and stopper firmly. Shake the bottle vigorously to mix. A flocculate (floc) precipitate will form if oxygen is present. The precipitate will be brownish-orange in color. A small amount of powdered reagent may remain stuck to the bottom of the bottle. This will not affect the results.
  7. Allow the sample to stand until the floc has settled about halfway in the bottle. Shake the bottle again. Let it stand once more until the upper half of the sample is clear.
  8. Use the clippers to open one Dissolved Oxygen 3 reagent powder pillow (found in the large round plastic container). Remove the stopper and add the contents of pillow 3. Carefully restopper the bottle. Check to make sure there are no air bubbles. Shake to mix. The floc will dissolve and an amber color will develop if oxygen is present.
  9. Fill the small round plastic measuring tube to the top with the amber colored sample water. This tube measures the correct amount of sample to be tested. Put the stopper back on the DO bottle with the extra amber colored sample water and set it aside. This extra sample water will not be used.
  10. Empty the tube of sample water into the square mixing bottle. Place the bottle on top of a white piece of paper so that the color change shows up better.
  11. Unscrew the top of the brown sodium thiosulfate bottle. Fill the eyedropper with the sodium thiosulfate. Hold the dropper straight up- and-down over the square mixing bottle and add one drop at-a-time into the amber colored water sample in the square mixing bottle. Swirl the bottle after each drop. Count the number of drops it takes to turn the water sample from amber to clear.
  12. Record the number of drops it took to turn the sample in the square mixing bottle to clear. Each drop is equal to 1 mg/1 of dissolved oxygen. For example, if it takes 8 drops to turn the sample clear, then there are 8 mg/1 of dissolved oxygen in the sample.
  13. When finished, pour the treated samples into the waste water bottle. Rinse the bottles and tube. Put everything back into the DO kit and return the kit to its container.

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