酸性氯酸钾处理-水浴加热全自动凯氏定氮仪测定土壤矿物中的固定态铵

固定态铵作为一种重要的潜在氮源，准确测定其含量，对于认识土壤肥力的形成机理、生态系统氮循环和保障国家粮食安全具有十分重要的意义。固定态铵最常用的方法是Silva-Bremner法，但该方法试剂配制要求严苛，前处理过程操作繁琐、费时。为了实现快速、准确、安全地测定土壤固定态铵的含量，对前处理过程进行了研究，用酸性氯酸钾溶液处理土壤样品，用水浴代替震荡，并与Silva-Bremner法的结果进行了对比。试验了自动凯氏定氮仪工作参数、酸性氯酸钾的浓度和用量、水浴加热的温度和时间，确定了测定土壤固定态铵的最佳条件。结果表明，称取1克样品加入20毫升氯酸钾-盐酸混合溶液（3％-10％）预处理，用0.5mol/L氯化钾溶液交换、洗涤，残渣加入加5mL氢氟酸-盐酸溶液（5mol/L-1mol/L），在沸水浴加热1.5-2h，用自动凯氏定氮仪蒸馏滴定。对5种类型土壤固定态铵7次测定的结果进行了数据分析，相对标准偏差（RSD）均小于3.87%，最大G值1.49，最大F检验值4.12，最大t检验值0.72，均小于临界值，两种方法测定结果无显著差异。该方法的操作安全性和分析效率得到大幅提高，方法的精密度、准确度满足要求。

Determination of Fixed Ammonium in Soil Minerals by Automatic Kjeldahl Nitrogen Analyzer with Acidic Potassium Chlorate Treated-Water Bath Heating

As an important potential nitrogen source, accurate determination of fixed ammonium content is of great significance for understanding the formation mechanism of soil fertility, ecosystem nitrogen cycle and ensuring national food security. The most commonly used method for fixed ammonium is the Silva Bremner method, but this method requires strict reagent preparation requirements, and the pre-treatment process is cumbersome and time-consuming. In order to achieve rapid, accurate, and safe determination of fixed ammonium content in soil, the pre-treatment process was studied. Soil samples were treated with acidic potassium chlorate solution, and water bath was used instead of shaking. The results were compared with those of the Silva Bremner method. The operating parameters of the automatic Kjeldahl nitrogen analyzer, the concentration and dosage of acidic potassium chlorate, the temperature and time of water bath heating were tested, and the optimal conditions for determining fixed ammonium in soil were determined. The results showed that 1 gram of the sample was pre treated with 20 mL of potassium chlorate hydrochloric acid mixed solution (3% -10%), exchanged and washed with 0.5mol/L potassium chloride solution, and the residue was added with 5 mL of hydrofluoric acid hydrochloric acid solution (5 mol/L-1 mol/L). The sample was heated in a boiling water bath for 1.5-2 hours, and then distilled and titrated with an automatic Kjeldahl nitrogen analyzer. The results of seven determinations of fixed ammonium in five types of soil were analyzed. The relative standard deviation (RSD) was less than 3.87%, the maximum G value was 1.49, the maximum F-test value was 4.12, and the maximum t test value was 0.72, which were all less than the critical value. There was no significant difference between the results of the two methods. The operational safety and analytical efficiency of this method have been greatly improved, and the precision and accuracy of the method meet the requirements.