Determination of Hydrolysable Nitrogen in Soil Samples by Alkaline Hydrolysis Diffusion Separation Acid-base Titration Based on a Polypropylene Diffusion Dish

BACKGROUND: The traditional alkaline hydrolysis diffusion separation acid-base titration method is used to determine the hydrolysable nitrogen in soil samples. Usually, a glass diffusion dish is used for alkaline hydrolysis diffusion separation. However, during sample pretreatment and alkaline hydrolysis diffusion separation, the operator often faces the following three problems. First, the solution in the inner chamber of the glass diffusion dish is very easily polluted by sodium hydroxide solution and alkaline glue solution. Second, ammonia leakage occurs easily between the glass diffusion dish and the cover, and it is often not possible to remedy when it is found. Third, the glass diffusion dish is bulky and fragile, and the experimental operation is inconvenient, all of which lead to the instability of measurement results due to inexperience of the operator.OBJECTIVES: To establish a new method for the determination of hydrolysable nitrogen in soil samples by alkaline hydrolysis diffusion separation acid-base titration based on polypropylene diffusion dish.METHODS: A polypropylene diffusion dish was used instead of a glass diffusion dish in the alkaline hydrolysis of hydrolysable nitrogen. The cleaning method and the sealing of the diffusion dish were improved. The addition amount of reducing agent and the concentration of sodium hydroxide solution（1.8mol/L） were unified. The addition volume of sodium hydroxide solution was appropriately increased, and the concentration of hydrochloric acid standard solution was reduced.RESULTS: The absolute deviation of reference materials GBW07416a with the measured value of hydrolysable nitrogen