Novel method for measuring Kjeldahl nitrogen

Abstract

The invention belongs to the technical field of Kjeldahl nitrogen measurement methods, and in particular relates to a novel method for measuring Kjeldahl nitrogen. The novel method for measuring Kjeldahl nitrogen achieves the purposes of measuring nitrogen content in a measured object by the following steps of: digesting the measured object according to a conventional Kjeldahl method to obtain a digestion solution, adding water to dilute the digestion solution and adding alkaline to obtain an alkaline digestion solution, heating and blowing off the digestion solution with gas, absorbing the blown-off gas with an absorption solution, and measuring the difference value between the electrical conductivities before and after the absorption by a conductivity meter.

Description

technical field [0001] The invention belongs to the technical field of determination methods for Kjeldahl nitrogen, in particular to a new method for determining Kjeldahl nitrogen. Background technique [0002] Nitrogen is the first of the three agricultural elements. Nitrogen has many forms in nature, so its determination is difficult. The Kjeldahl nitrogen method can measure all forms of nitrogen except nitrate nitrogen and nitrite nitrogen, so it is one of the most commonly used methods for determining nitrogen. Kjeldahl nitrogen refers to using concentrated sulfuric acid as a medium to mix soil, Various forms of nitrogen (except nitrate nitrogen and nitrite nitrogen) in samples such as plants are digested into ammonium nitrogen at high temperature. Kjeldahl nitrogen includes ammonia nitrogen and organic nitrogen compounds that can be converted into ammonium salts under these conditions. Such organic nitrogen compounds mainly include proteins, amino acids, peptides, pept...

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Problems solved by technology

In this way, it is necessary to heat the test solution to 100°C, and then continue to distill, which consumes electricity and time, and a large amount of water is distilled at the same time. Diluting ammonia is not conducive to the determination of low-concentration nitrogen.

[0006] The measurement method after such separation is currently: if the amount of ammonia is relatively high, boric acid is added to the absorption solution, and then sulfuric acid is used to titrate the amount of ammonia. The end point of the titration is judged by visual method or potentiometric method. For the titration with weak base, the jump of titration is not obvious, and the end point of visual method is difficult to judge even if mixed indicator is used, and the titration error is relatively large, while the potentiometric method requires a full set of potentiometric titration instruments. That way the cost is high, and the equipment occupies a large area; if the amount of ammonia is very low, after the absorption liquid is fixed to volume, add a color developer, etc. to measure the concentration of ammonia by photometric method (colorimetry), but the color developer used It is more complex and contains mercury-containing chemical reagents, which not only increases the cost of determination but also causes secondary pollution

[0007] The above-mentioned existing determination method has low measurement accuracy, which can only reach 0.1mgN; poor reproducibility: 1% (relative amount is not provided); the separation process is complicated and the operation is cumbersome, and each (each) test tube needs to be separated by high temperature distillation during separation , a test tube sample (distillation) separation (test) is completed, the test tube needs to be replaced manually (without automatic sample injection); the separation process is dangerous: when separating, each (each) test tube needs to be injected with a large amount High temperature steam, strong alkali, the system (glass test tube) is prone to problems, causing danger or injury

Therefore, the existing equipment manufacturers are emphasizing that their products add a set of safe operating system; energy consumption: A, power consumption: main engine power 2200W, takes 6 minutes; B, water: 2L / min, takes 4 minutes; automatic sample injection is complex : (At present, only a few foreign manufacturers realize automatic sampling) Because ammonia recovery is required to be completed in a closed environment to realize automatic sampling, the system is bulky (about 1000*900*800mm, about 50-60 samples), and the cost is expensive

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