TIÊu chuẩn xây dựng tcxd 81: 1981

2.17.7. Result calculation

Concentration of nitrite ion (NO₃) is expressed as mg/l and calculated as follows:

Where:

v - volume of water sample, expressed as ml;

50 - Volume of water sample that has color, expressed as ml.

2.18. Ammonia and ammonium

2.18.1. Scope of application

This method is meant for determination of ammonia and ammonium in water that does not contain amines, chlorine, chloramine, acetone, alcohol, and other organic substances that react with Netle indicator. Determination of ammonia and ammonium is obstructed by muddy water, high concentration of iron and sulfur.

2.18.2. Nature of the method

Ammonia and ammonium ions react with potassium iodua mercury in an alkaline environment and create a brownish yellow precipitate.

2.18.3. Chemicals

+ Distilled water without ammonia.

+ Netle indicator: 100g.

Hg₂I analytical grade and 70g K.I analytical grade mixed with sodium hydroxide solution. Sodium hydroxide solution is prepared as follows: dissolve 160g of a.g. NaOH in 500 ml of distilled water. Add more distilled water until the volume reaches 1 liter. Leave the solution to deposit precipitates for at least 4 hours and use only the part that is transparent.

+ Sodium potassium tartrate, 50% solution: Dissolve 50 g of a.g. KNC₄H₄O₆.4H₂O in dissolved water; dilute the solution with distilled water until the volume reaches 100 ml; add 0.2 - 0.5 ml of netle indicator. Leave the solution to deposit precipitates and use the transparent part of the solution.

Komplexon III, 50% solution: Dissolve 10 g of a.g. sodium hydroxide in 60 ml of distilled water, then add 50 g of komplexon III. Add more distilled water until the volume reaches 100 ml.

+ Sodium hydroxide, 15% solution.

+ Ammonia chloride.

Solution I: Dissolve 0.2965g of a.g. NH₄Cl in distilled water to create 1 liter of solution. Every ml of this solution contains 0.100mg NH₄. Only prepare this solution before use.

Solution II: dilute 50 ml of solution I with distilled water until the volume reaches 1 liter. Every ml of this solution contains 0. 005mg NH₄. Only prepare this solution before use.

2.18.4. Drawing standard graph

Successively add distilled water to dilute 0; 0.5; l,0; 2.0; 4.0; 6.0; 8.0; 10; ... 40ml of solution II until the volume reaches 50 ml, and test each of them the same way as water sample. Respective concentrations of the new solutions are 0;0.05; 0.10; 0.20; 0.40; 0.60; 0.80; 1.00; ...; 4.00 mg/l NH⁴⁺. Measure the color intensity of each solution with a photoelectric colorimeter.

Draw a standard graph based on the measured optical density of the solutions. The vertical axis indicates optical density, the horizontal axis indicates corresponding concentration (mg/l).

2.18.5. Standardized color chart

Successively add distilled water to dilute 0; 0.5; 1.0; 2.0; 4.0; 6.0; 8.0; 10.0; ...; 20 ml of solution II in netle cylinders. Test the solutions successively in the same way as testing water sample. Respective concentrations of the new solutions are 0; 0.05; 0.10; 0.20; 0.40; 0.60; 0.80; 1.00; ...; 2.00 mg/l NH⁴⁺

2.18.6. Running the test

Add 1 - 2 drops of komplexon III or sodium potassium tartrate to 50 ml of water sample and shake it gently. Add 0.5 - 1 ml of 1 - 2 drops of komplexon III or sodium potassium tartrate if water hardness is high. Add 1 ml of netle indicator and share gently. Measure the color intensity of the solution using the photoelectric colorimeter after 10 minutes; use a green filter glass (O = 400: 425mm, cuvet thickness = 1 - 5 cm), or compare the color with the standard color chart with bare eyes. After 30 minutes from the appearance of the color, the color of the solution must not change. When measuring color intensity with photoelectric colorimeter, if the ammonium ion concentration is higher than 6 mg/l, the solution must be diluted before being measured.

2.18.7. Result calculation

Ammonium ion concentration (NH⁴⁺) is expressed as mg/l and calculated as follows:

Where:

V - Volume of tested water, expressed as ml;

50 - Volume of diluted water sample, expressed as ml.

2.19. Calculation of dried dregs at 105⁰C

2.19.1. Running the test

Leave 200 ml of water sample to evaporate in a ceramic bowl, which has been dried at 105⁰C, on a double boiler until it dries out. Dry the ceramic bowl with dried dregs for 2 hours at 105⁰C, stabilize the temperature in a desiccator and weigh it until its weight remains unchanged.

2.19.2. Result calculation

The concentration of dregs dried at 150⁰C is expressed as mg/l and calculated as follows:

Where:

V - Volume of water sample, expressed as ml.

2.20. Concentration of insoluble dregs dried at 105⁰C

2.20.1. Running the test

Filter 200 ml of water sample with filter paper, which has been dried at 105⁰C, then weigh it until its weight remains unchanged. Dry the filter paper with dried dregs for 2 hours at 105⁰C, stabilize the temperature in a desiccator and weigh it until its weight remains unchanged.

2.20.2. Result calculation

The concentration of dregs dried at 105⁰C is expressed as mg/l and calculated as follows:

Where:

V - volume of water sample, expressed as ml

2.21. Concentration of insoluble dregs burnt at 600⁰C

2.21.1. Running the test

Put the filter paper that contain insoluble dregs dried at 105⁰C (see 2.20) in a ceramic bowl with known weight; heat it at 600⁰C for 1 hour; stabilize the temperature in the desiccator and weigh it until its weight remains unchanged.

2.21.2. Result calculation

The concentration of dried dregs burnt at 600⁰C is expressed as mg/l and calculated as follows:

Where:

V - Volume of water sample, expressed as ml.