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Water What-ifs

Instructions for LaMotte Water Test Kits

pH Test Kit pH should be measured immediately after collection because a change in temperature can affect the pH levels.
  1. Rinse the test tube with sample water.
  2. Fill the test tube (0230) to the 5 ml mark with sample water.
  3. Holding the dropper bottle vertically, add ten drops of indicator solution to the test tube with the sample water.
  4. Cap and invert three times.
  5. Place test tube into Octet Comparator. Match sample color to a color standard. Record pH number off of the Octet Comparator.
NOTE: If more than one pH reading is taken, report the most common value, the mode, rather than the average.

Normal values for most freshwater systems are 6.5-8.5.


Dissolved Oxygen Test Kit Goggles and gloves should be worn while performing the dissolved oxygen tests.

Sampling Method

  1. Rinse the sampling bottle (0688-DO) with the sample to be tested.
  2. Replace the top on the empty sampling bottle and submerge it in water sample to be tested.
  3. After submerging the sampling bottle, remove the top under the water and fill the bottle while tapping the sides to release the air bubbles.
  4. Replace top while the bottle is submerged.
  5. Remove the full, capped bottle from the water and remove the top.

Preserving (fixing) Sample for Testing

  1. Add 8 drops of Manganous Sulfate Solution (4167) to the bottle of sample water.
  2. Add 8 drops of Alkaline Potassium Iodide Azide (7166) to the bottle of sample water. Put the top on the bottle and invert 2 or 3 times. A precipitate will form and should be allowed to settle below the shoulder of the bottle before continuing with the next step.
  3. Use the 1.0 gram measuring spoon (0697) provided with the kit to add 1 gram of Sulfamic Acid Powder (6286).
  4. Put the top on the bottle and invert to mix until the precipitate is dissolved. A clear yellow to orange brown color will develop depending on the oxygen content of the sample.
  5. The sample is now "fixed" and ready to be tested.
NOTE: Once the sample is fixed, contact between the sample and the atmosphere will not affect test results.

Testing the Water Sample

If the color of the fixed sample is already a faint yellow, skip steps #3 and #4 and continue with the second part of step #5 which is the addition of Starch Indicator Solution.

  1. Fill the titration tube (0299) to the 20 ml mark with the fixed sample.
  2. Fill the Direct Reading titrator (0377) with Sodium Thiosulfate (4169).
  3. Place the titrator in the top of the titration tube and add one drop of the Sodium Thiosulfate and swirl.
  4. Continue to add Sodium Thiosulfate dropwise until the sample is a faint yellow.
  5. Remove the top of the titration tube and the titrator. Add 8 drops of Starch Indicator Solution (4170WT). This will cause the sample to turn blue.
  6. Replace the top of the titration tube and the titrator. Continue to add Sodium Thiosulfate dropwise until the blue color disappears.
  7. Read the titrator scale in parts per million (ppm).

NOTE:If the titrator is empty (10 ppm) and a color change has not been observed, refill the titrator with Sodium Thiosulfate and continue the titration until the color change occurs.

If more than one dissolved oxygen reading is taken, take average of all the readings and record that number.

Most natural water systems require 5-6 parts per million of dissolved oxygen to support adiverse population.


Nitrate & Phosphate Test Kit

Nitrate

  1. Fill the test tube (0844) to the 2.5 ml mark with the water sample.
  2. Add Mixed Acid Reagent (V-6278) to the water sample to the 5 ml mark.
  3. Cap and invert three times. Wait 2 minutes.
  4. Using the 1.0 gram measuring spoon (0699) provided with the test kit, add one level spoon of Nitrate Reducing Reagent (V-6279). Cap and invert 30-40 times in a one minute period. Wait 10 minutes.
  5. Mix after the 10 minute waiting period and remove the cap.
  6. Insert the tube into the Nitrate-N and Phosphate Comparator (3120) with the Axial Reader (2071).
  7. Match the sample color to a color standard.
  8. Read the number off the Nitrate-N and Phosphate Comparator and record as Nitrate-Nitrogen in parts per million (ppm).
  9. To convert to Nitrate, multiple by 4.4.

NOTE:Reading off Nitrate-N and Phosphate Comparator x 4.4 = mg/L or ppm Nitrate.

If more than one nitrate reading is taken, take the average of all the readings and record that number.

This test will measure a range of Nitrate-Nitrogen from 0.2-1.0 ppm.


Phosphate

NOTE: This test should be run on clear samples only. Filter sample if necessary.

  1. Fill the test tube (0844) to the 10 ml mark with sample water.
  2. Use the 1.0 ml pipet (0354) provided with the water test kit to add 1.0 ml to Phosphate Acid Reagent (V-6282).
  3. Cap the test tube and invert three times.
  4. Use the 0.1 gram spoon (0699) to add one level measure of Phosphate Reducing Reagent (V-6283). Cap and invert until the reagent is dissolved. Wait 5 minutes.
  5. Remove the cap. Place the test tube in the Nitrate-N and Phosphate Comparator (3120) with the Axial Reader (2071).
  6. Match the sample color to the color standard.
  7. Record the result as ppm Total Phosphate.

NOTE:If more than one phosphate reading is taken, take the average of all the readings and record that number.

Total phosphate levels of non-polluted waters are usually less than 0.1mg/L or ppm.

NOTE: All the waste generated by the LaMotte test procedures may be poured down the drain with the water running to dilute it. The only time the waste may not be disposed of in this manner is if the waste generated is from 30 or more tests for a single parameter.

For example, if 30 students all use the LaMotte test kit to test the dissolved oxygen levels of a sample, the waste cannot be poured down the drain. A waste management facility should be contacted to determine the correct method of disposal.

But if 10 students test for pH, 10 students test for nitrates and 10 students test for dissolved oxygen, the waste generated by this group can be disposed of down the drain with the water running to dilute it.

If the tests are done in the field, carry a waste container with a lid along with the kits. Pour all the waste into the container and save it for appropriate disposal at a later time.


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©1998 April J. Cleveland for Science Junction, NC State University.
All rights reserved.
page design by Lisa Leonor Grable and April J. Cleveland
URL: http://www.ncsu.edu/sciencejunction/depot/experiments/water/lamotte.html
Last Modified: 5/15/01

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