Several factors influencing total nitrogen less than ammonia nitrogen
1. The error caused by the experimental environment is in the surrounding environment of the laboratory, such as toilets or ammonia storage rooms. The laboratory air contains a small amount of ammonia and is easily soluble in water. Therefore, the experimental water also contains ammonium ions to varying degrees. In the experimental analysis, the preparation and preservation of diluted ammonia-free water is often neglected, which causes the external ammonia nitrogen to dissolve in the water sample and increases the concentration error of the ammonia nitrogen in the water sample.
2. The sampling error is caused by the continuous changes of the nitride in the water. After collection, the samples were sent back to the laboratory for experimental analysis. Their storage time, storage location, light, and even the sampling order of the analyst will bring different errors to the experimental analysis of ammonia nitrogen and total nitrogen.
3. In the error experiment of reagent and water introduction, the first step is to purify the potassium persulfate solution. The absorbance of the unpurified potassium persulfate solution is much greater than that of the purified potassium persulfate solution, and the standard deviation of the purified potassium persulfate solution is small, which has little effect on the deviation of the water sample measurement results.
The success or failure of the total nitrogen experiment is directly related to the quality of water and reagents.
The first is the experimental water. Ordinary distilled water cannot meet the requirements and must be re-distilled. When using homemade ammonia-free water, avoid contact with ammonia in the laboratory air, and be contaminated with ammonia again during the storage of water. The quality of potassium persulfate is related to the success of the entire experiment. The purity of potassium persulfate is related to the blank value and the accuracy of the measurement results. The results show that Merck's potassium persulfate can meet the experimental requirements.
4. Errors introduced by the experimental method The analysis of ammonia nitrogen usually uses the classical Nessler reagent photometry. Although the color development requires an alkaline environment, the pretreatment process is relatively simple. After the color development is directly measured, the result can be calculated. Relatively speaking, the pretreatment process for the analysis of total nitrogen is more complicated. It needs to undergo 30min pressurization under alkaline conditions. If the sealing is not good during the pretreatment process, it will also lead to the release of ammonia nitrogen under high temperature and high pressure. Few laboratories have used raw materials with sealed stoppers for the digestion of total nitrogen, so the conversion cannot be 100% conversion, which will lead to the release of ammonia nitrogen in the process of total nitrogen, causing errors.
5. Error introduced by sample turbidity The turbidity effect that can be eliminated by the pre-treatment of the total nitrogen analysis cannot be eliminated in the ammonia nitrogen analysis. In addition, different colorimetric cuvettes are commonly used in colorimetry. The combination of these factors affects the final result. Come difference. Since both test methods are used to measure absorbance, the turbidity caused by suspended matter in the sample is the most difficult influencing factor in the sample analysis. In the experimental analysis and determination of total nitrogen and ammonia nitrogen, the pretreatment of the total nitrogen analysis can be eliminated The effect of turbidity cannot be eliminated in the analysis of ammonia nitrogen, which may cause a higher situation in the detection of ammonia nitrogen in water samples.
6. Errors introduced by different analysis methods and analytical instruments Almost all analytical experimental methods have certain method errors in measuring samples. The experimental analysis of total nitrogen and ammonia nitrogen is no exception. The Nessler reagent photometric method for analyzing ammonia nitrogen has errors. The alkaline persulfate decomposition method of nitrogen also has errors. The errors of the two analysis methods bring great errors to the final measurement results. Various instruments, colorimetric tubes, cuvettes and other instruments used in the entire analysis process of the two projects may introduce different degrees of errors; the sensitivity of the spectrophotometer used in colorimetry, The precision and accuracy may not be the same, and the size of the error introduced is also different. Especially for the colorimetric determination of total nitrogen and ammonia nitrogen, light in two different light regions, visible and ultraviolet, is used, which introduces a greater difference in error.
7. Errors introduced by data processing In data processing, there are two possible errors: One is the error introduced by different calibration curves. Although the two curves used in these two projects are all qualified by statistical inspection, the curves and the curves have Differences, this difference brings errors; the second is to introduce errors to the choice of significant figures. The sum of the two errors forms a large error between the two analysis items. The smaller the concentration of the sample, the greater the error. This is the case in which, in diluted water samples, ammonia nitrogen is less than total nitrogen.
8. There are various error experimental methods caused by different personnel factors, and there will be different differences in error control: from the above analysis, it can be seen that the errors of ammonia nitrogen and total nitrogen in the laboratory process are objective and subjective. Influenced by many factors, the comprehensive error will lead to the situation that ammonia nitrogen may exceed total nitrogen.
How to prevent erroneous data caused by errors
In summary, in the detection of sewage, ammonia nitrogen and total nitrogen will often appear in the ammonia nitrogen is higher than the total nitrogen, it is inevitable, especially in some of the total nitrogen, ammonia nitrogen accounts for a large proportion of water In the sample, due to the existence of various induced errors, the probability of this situation is very high. The testing personnel should keep the analysis time of total nitrogen and ammonia nitrogen consistent to eliminate the interference of drug samples and experimental condition