O-S-801F
4.3.19 Nitrate.
4.3.19.1 Standard nitrate solution. Prepare a stock nitrate solution by dissolving 0.625 g of potassium nitrate in water in a 1 liter volumetric flask and make up to volume. Prepare a
standard nitrate solution by pipeting 20 ml of the stock solution into a 1 liter volumetric flask and make up to volume. (The standard solution contains 0.00766 mg of nitrate per milliliter.)
4.3.19.2 Class 1. Pipet 10 ml of water into one of a matched pair of Nessler tubes and add, by pipet, 5 ml of class 1 specimen and 15 ml of nitrate free reagent sulfuric acid. Into the second Nessler tube, pipet 4 ml of water and 6 ml of the standard nitrate solution prepared in 4.3.19.1. Add, by pipet, 20 ml of nitrate free reagent sulfuric acid. To each Nessler tube, add 0.5 ml of a saturated solution of ferrous sulfate and mix. Immediately after mixing, the color or darkening of the solution in the Nessler tube containing the class 1 specimen shall not exceed that of the solution in the Nessler tube containing the standard nitrate solution. (Note: Only the difference
in color is to be considered, not the turbidity which may be present due to the precipitation of lead sulfate when the specimen is diluted.)
4.3.19.3 Class 2. Pipet 10 ml of class 2 specimen into one of a matched pair of Nessler tubes and add, by pipet, 10 ml of nitrate free reagent sulfuric acid. Into the second Nessler tube, pipet
5 ml of the standard nitrate solution prepared in 4.3.19.1 and add, by pipet, 15 ml of nitrate free reagent sulfuric acid. To each Nessler tube, add 0.5 ml of a saturated solution of ferrous sulfate and mix. Immediately after mixing, the color or darkening of the solution in the Nessler tube containing the class 2 specimen shall not exceed that of the solution in the Nessler tube containing the standard nitrate solution. See note in 4.3.19.2.
4.3.19.4 Class 3. Pipet 15 ml of class 3 specimen into one of a matched pair of Nessler tubes and add, by pipet, 5 ml of nitrate free reagent sulfuric acid. Into the second Nessler tube, pipet
5 ml of the standard nitrate solution prepared in 4.3.19.1 and add, by pipet, 15 ml of nitrate free reagent sulfuric acid. To each Nessler tube, add 0.5 ml of a saturated solution of ferrous sulfate and mix. Immediately after mixing, the color or darkening of the solution in the Nessler tube containing the class 3 specimen shall not exceed that of the solution in the Nessler tube containing the standard nitrate solution. See note in 4.3.19.2.
4.3.19.5 Class 4. Pipet 20 ml of class 4 specimen into one of a matched pair of Nessler tubes and add, by pipet, 10 ml of nitrate free reagent sulfuric acid. Into the second Nessler tube, pipet
5 ml of water and 5 ml of the standard nitrate solution prepared in 4.3.19.1 and add, by pipet,
10 ml of nitrate free reagent sulfuric acid. To each Nessler tube, add 0.5 ml of a saturated solution of ferrous sulfate and mix. Immediately after mixing, the color or darkening of the solution in the Nessler tube containing the class 4 specimen shall not exceed that of the solution in the Nessler tube containing the standard nitrate solution. See note in 4.3.19.2.
4.3.20 Ammonium. As applicable, dilute 20 ml of class 1, 49 ml of class 2, 58 ml of class 3, or
78 ml of class 4 specimen to 100 ml in a volumetric flask. As applicable, in a Nessler tube, dilute 20 ml of class 1 or class 2 specimen dilution or dilute 25 ml of class 3 or class 4 specimen dilution to 90 ml with water, make alkaline with sodium hydroxide solution, and add 1 ml of Nessler's reagent. The color produced shall not exceed that produced by 0.072 mg of ammonium
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