Determination of total nitrogen in water

Determination of total nitrogen in water is an important environmental monitoring method. Total nitrogen is the sum of all nitrogen-containing organic matter and inorganic nitrogen in water, including both nutrients beneficial to biological growth and pollutants that will destroy biological ecological environment. Therefore, the determination of total nitrogen in water is very important for protecting the environment and maintaining human health. This paper introduces a commonly used method for determining total nitrogen in water-Kjeldahl method.

1. principle

Kjeldahl nitrogen determination method takes amino acids as standard substances, and converts all organic nitrogen and inorganic nitrogen in water into ammonium salt, then decomposes ammonium salt into ammonia gas, and titrates with acid to calculate the concentration of total nitrogen. This method is suitable for high concentration of total nitrogen in water samples.

2. Experimental steps

(1) sample processing

Add the water sample into a beaker, add a proper amount of sodium hydroxide under the ventilation condition, detect it to be neutral with potassium iodide, then add a proper amount of ammonium chloride and copper chloride solution to neutralize the sodium hydroxide, and distill and collect the distillate.

(2) distillation

Pour the sample into a kjeldahl distiller for distillation. First, heat the water sample to boiling, then heat it until the sample is dry, then add 40% sodium hydroxide, and continue heating until the color of water droplets in the collector becomes lighter.

(3) titration

Add the distillate into the acid for titration until the color of the liquid turns pale yellow after dropping HCl. Then calculate the total nitrogen concentration.

3. Preventive measures

(1) Avoid contact with acid and alkali in the experiment.

(2) In order to prevent ammonia leakage, the experiment should be conducted in a well-ventilated place.

(3) Ensure that the distillation time is enough to fully separate the nitrogen in the sample.

(4) Pay attention to the titration speed to avoid adding the wrong amount.

In a word, there are many methods to determine total nitrogen in water, and kjeldahl method is one of the more traditional, simple and accurate methods. Before the experiment, the required materials and equipment should be fully prepared and carried out in strict accordance with the experimental steps to ensure the accuracy of the experimental results.