基于聚丙烯扩散皿的碱解扩散分离-酸碱滴定法测定土壤中水解性氮

陆迁树; 刘振超; 曾仕秀; 宋安邦; 李志雄; 张松; 张帅; 兰明国

doi:10.15898/j.cnki.11-2131/td.202201180013

基于聚丙烯扩散皿的碱解扩散分离-酸碱滴定法测定土壤中水解性氮

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

摘要

摘要: 传统的碱解扩散分离-酸碱滴定法测定土壤样品中的水解性氮，通常采用玻璃扩散皿进行碱解扩散分离。但是使用该法对样品进行前处理和碱解扩散分离过程中，操作者常会面临如下三种困扰：一是玻璃扩散皿内室溶液极易被氢氧化钠溶液和碱性胶液污染；二是玻璃扩散皿和盖子之间容易出现氨气泄漏，而且发现时往往无法解决；三是玻璃扩散皿比较笨重易碎，实验操作不方便；最终导致测定结果不稳定性和操作者对该法体验不佳。本文采用聚丙烯扩散皿，通过改进扩散皿清洗方法和提升扩散皿密封性、统一还原剂加入量和氢氧化钠溶液浓度(1.8mol/L)、适当增加氢氧化钠溶液的加入体积和降低盐酸标准溶液浓度，提高了水解性氮测定的稳定性和准确性。该方法中发生的污染明显降低，避免了发生氨气泄漏，操作便捷。应用于分析土壤有效态标准物质的测定值与标准值一致，如水解性氮测定值< 50mg/kg的标准物质GBW07416a，其绝对偏差为0.2~1.8mg/kg；水解性氮测定值在50~200mg/kg的标准物质GBW07415a、NSA-1、NSA-4、NSA-5、NSA-6，其绝对偏差为0~4.0mg/kg。还原剂对硝态氮转化为铵态氮的加标回收率在89.6%~96.4%之间。该方法可满足测定土壤样品中水解性氮含量的要求。

Abstract:
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 < 50mg/kg was 0.2-1.8mg/kg. The absolute deviation of reference materials GBW07415a, NSA-1, NSA-4, NSA-5 and NSA-6 with the measured value of hydrolysable nitrogen of 50-200mg/kg was 0-4.0mg/kg. The recovery rate of nitrate nitrogen converted to ammonium nitrogen by reducing agent was 89.6%-96.4%. The measured value of soil available reference materials was consistent with the standard value.
CONCLUSIONS The stability and accuracy of hydrolysable nitrogen determination are improved. The pollution in this method is significantly reduced, ammonia leakage is avoided, and the operation is convenient. The method meets the requirements for determining the content of hydrolysable nitrogen in soil samples.

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