Notes On Dissocted Oxygen Measurement

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Register to read the introduction… Collect the sample to be tested in a 300 mL BOD bottle taking special care to avoid adding air to the liquid being collected. Fill bottle completely and add stopper.

2. Remove bottle stopper and add 1 mL of the manganous sulfate solution at the surface of the liquid.

3. Add 1 mL of the alkaline-potassium iodide-sodium azide solution at the surface of the liquid.

4. Replace the stopper, avoid trapping air bubbles and shake well by inverting the bottle several times. Repeat shaking after floc has settled halfway. Allow floc to settle a second time.

5. Add 1 mL of concentrated sulfuric acid by allowing the acid to run down the neck of the bottle above the surface of the liquid.

6. Restopper, rinse the top of the bottle to remove any acid and shake well until the precipitate has dissolved.

7. Titrate a volume of treated sample which corresponds to 200 mL of the original sample. This corrects for the loss of some sample during the addition of reagents. This volume calculated using the formula:

mL of sample to titrate = 200 x [300/(300-2)] = 201 mL

8. Pour 201 mL of sample from the BOD bottle into an Erlenmeyer
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Quiz 4.3

1. What equipment, apparatus or instrumentation is required for the DO determinations by the membrane electrode method?

2. What are the accepted methods of calibration of the DO meter and electrode?

3. What interferences can affect DO determinations by the membrane electrode procedure?

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Section 10: QA/QC

A Quality Assurance/Quality Control program is required by the NPDES permit. Quality Assurance (QA) is a set of operating principles that must be followed during sample collection and analysis. Lab bench sheets must be maintained that document when the sample was collected, how it was preserved, and what results were obtained.

Quality Control (QC) includes any testing which is done to prove that the results are reliable. One of every ten samples analyzed should be a Quality Control check. This may include duplicate samples, spike samples, reagent blank analyses and known QC samples obtained from outside

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