杜马斯-碳氮分析仪法测定缓控释氮肥释放氮量

Determination of nitrogen release from slow and controlled-release fertilizers by Dumas process using TOC/TN analyzer

为了提高缓控释氮肥释放氮量的测定效率,避免样品消煮过程中的强酸与毒害气体物质等问题,该研究基于杜马斯法原理,利用碳氮分析仪,测定2种缓控释氮肥在25℃静水释放试验中,第1、3、7、14和28天肥料浸出液的氮浓度,计算缓控释氮肥释放氮量,并与传统常规的凯氏蒸馏滴定法测定结果间进行比较。结果表明:2种方法肥料浸出液中N浓度测定结果之间呈极显著线性相关关系,相关系数r=0.991(n=30,P<0.01)。依据2种方法测定结果计算的氮素养分释放期彼此相差小于20%,符合国家标准《GB/T 23348-2009缓释肥料》及化工行业标准《HG/T 4215-2011控释肥料》的允许差范围。相比较传统的凯氏蒸馏滴定法,杜马斯-碳氮分析仪法测定缓控释氮肥释放氮量过程简便快捷,样品无需消煮,不涉及强酸不产生有毒有害物质。该结果为缓控释氮肥释放氮量新的测定方法提供了科学依据。

The Kjeldahl distillation-titration method（KDTM） is a standard method used by most laboratories to measure total nitrogen（N） in the Kjeldahl digests of fertilizer samples. However, the KDTM procedure generally is labor intensive and time-consuming for sample digestion process, in which concentrated acids and poisonous gas have a negative impact on the environment and health of laboratory operators. The purpose of this article was to investigate whether the methods of Dumas process（total organic carbon/total nitrogen analyzer, TOC/TN analyzer） can be used to determine N contents in the release solutions from slow/controlled release nitrogen fertilizers（S/CRNFs）. Two kinds of S/CRFs with 43.2% and 37.3% of total N content were selected. The solutions containing 10% of S/CRNFs were collected after incubating at 25℃ for 1, 3, 7, 14 and 28 days, respectively. In the TOC/TN analyzer, the solution samples diluted 400 times were oxidized in the combustion tube in the presence of oxygen at high temperature（800℃） using Pt as catalyst. We compared the N values measured by Dumas method and KDTM procedure. The result showed that a linear relationship can best describe the measured N concentration generated by both methods： y（Dumas-N）=0.905 x（Kjeldahl-N）＋0.040. The Pearson＇s correlation coefficient was 0.991 with a significance level（n=30, P〈0.01）. Paired samples t-test indicated that there was no significant（P〉0.05） difference of the N release contents of the S/CRFs measured by TOC/TN analyzer and KDTM method. Cumulative N release rates of two fertilizers after incubating for 14 and 28 days determined by TOC/TN analyzer were higher than that by KDTM method. However, a positive linear correlation with r=0.997（n=30, P〈0.01） was verified between the two methods. The regression equation was y（TOC/TN analyzer）=0.908x（KDTM method） ＋0.818. Thus the results suggested that measured N release of S/CRNFs by TOC/TN analyzer agreed very well with that measured by KDTM method. The N release period is an important parameter for assessing the quality of the S/CRNFs. The relative percentage difference of the N release periods of the S/CRNFs was less than 20% between the two N determination methods, which was the acceptance criteria for evaluating the N release period with the national standards ＂GB/T 23348-2009 slow-release fertilizer＂ and the chemical industry standard ＂HG/T 4215-2011 controlled-release fertilizers＂. It is suggested that the TOC/TN analyzer according to Dumas principle can be an alternative to the labor-intensive and time-consuming KDTM procedure for measuring N release of S/CRNFs. The TOC/TN analyzer is easy to handle and no preparation of sample digestion for N analysis is necessary.