During water quality testing, analysts may encounter a counterintuitive phenomenon: the measured value for ammonia nitrogen exceeds that of total nitrogen. Based on testing principles, total nitrogen encompasses various forms—such as ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen—meaning the total nitrogen value should generally not be lower than the ammonia nitrogen value. When this situation arises, analysts should examine the testing process to determine whether the ammonia nitrogen result is erroneously high or the total nitrogen result is erroneously low, and then take appropriate measures based on the specific cause.
Common causes of high ammonia nitrogen readings
When using ammonia nitrogen analyzers or related reagents, the color development stage can be affected by various factors, leading to results that exceed actual values.
1. Color development status: If the water sample exhibits abnormal color changes (e.g., the color is excessively dark or deviates from expectations) after the reaction is complete, this may indicate the presence of interfering substances.
2. Interference from color and turbidity: If the water sample itself is colored or turbid, it may affect the readings during the colorimetric analysis stage. …causing the measured results to be higher than actual values.
III. Metal ion interference: Certain metal ions may undergo side reactions with the reagents, thereby affecting the stability of the color-forming reaction.
IV. Organic matter interference: Complex organic substances present in the water sample may also interfere with the color development process.
In light of the above, the technical team at Lianhua Technology recommends the following: appropriately pretreat the water sample before testing, or consult a Lianhua Technology after-sales engineer to identify the specific type of interference and quickly pinpoint the cause of the anomalous results.
Common causes of low total nitrogen measurement results
The procedure for determining total nitrogen involves multiple steps, and any stage can influence the final result. The following situations are likely to lead to low total nitrogen readings:
I. Incomplete oxidation: This is a relatively common cause. During the digestion process, if the concentration of reducing substances is high, or if the digestion temperature or duration is insufficient, nitrogen-containing compounds may not be fully oxidized to nitrates, resulting in lower values.
Lianhua Technology K20 tablets are recommended.
Core application: Specialized digestion tablets for total nitrogen testing in water quality analysis; they serve as a substitute for traditional liquid potassium persulfate reagents and are compatible with HJ standards. …Standard 636-2012.
Applications: Digestion for Total Nitrogen analysis in surface water, sewage, industrial wastewater, etc.; demonstrates significant resistance to interference from water samples with high organic content.
II. Turbidity interference: If the digested water sample remains turbid, it may exhibit high absorbance at critical wavelengths, thereby affecting the measurement results.
III. Organic matter or unknown interfering substances: Certain specific organic compounds or impurities may cause the water sample to become turbid after digestion, similarly leading to abnormal absorbance readings.
IV. Issues related to operation, reagents, or instruments: It is recommended to verify performance using standard solutions to ensure results fall within the permissible margin of error.
Operational recommendations from Lianhua Technology
To address potential issues of incomplete oxidation during Total Nitrogen determination, Lianhua Technology recommends the following:
1. Confirm that the digestion temperature and duration align with the operating instructions of the water quality testing instrument being used;
2. For water samples with high levels of reducing substances, consider appropriate dilution prior to measurement;
3. Use Lianhua Technology’s Total Nitrogen analyzers and matching pre-prepared reagents to help minimize human error and enhance the reliability of results.
Lianhua Technology was founded in 1982. The company is an innovative environmental protection enterprise specializing in the R&D, production, sales, and service of water quality testing instruments. Headquartered in Beijing, it maintains branches and offices in 30 regions across the country. With an R&D team comprising over 30% of its workforce and a wealth of accumulated testing data and solutions across various industries, the company is dedicated to providing China’s water quality guardians with professional, intelligent testing instruments and comprehensive, attentive service support, including 24-hour technical assistance.
Summary
When a water sample shows an ammonia nitrogen level higher than the total nitrogen level, it is recommended to investigate the issue from two perspectives:
1. Ammonia nitrogen reading is erroneously high: Check if color development is normal and verify the absence of interference from color, turbidity, metal ions, or organic matter.
2. Total nitrogen reading is erroneously low: Assess whether digestion is complete, check for turbidity or unknown interfering substances in the water sample, and verify that the operating procedures and instruments are functioning correctly.
Systematic troubleshooting and adherence to standardized operating procedures generally allow for the identification of the cause and the implementation of appropriate corrective measures.
Note: The experimental procedures described herein are based on general testing principles. Variations may exist depending on the water sample matrix; therefore, method validation is recommended prior to actual operation.
Post time: Sep-17-2026
