Ammonia nitrogen enrichment in water will affect the biological growth of water. Therefore, ammonia nitrogen index is a must-check item in environmental monitoring, including groundwater environmental quality standards, surface water environmental quality standards, national drinking water hygiene standards, integrated wastewater discharge standards, and pulp and paper. Industrial water pollutant discharge standards, pollution control standards for domestic waste landfills, etc. At present, ammonia nitrogen determination methods mainly include spectroscopy, titration, electrochemical analysis, flow injection, chromatography, etc. Among them, the national standard is based on spectroscopy, mainly involving Nessler's reagent colorimetry and salicylic acid spectrophotometry. However, the Nash's reagent colorimetric method requires the use of the highly toxic substance mercury iodide, which has an impact on the environment. Relatively speaking, the salicylic acid spectrophotometry is environmentally friendly and the detection limit is low. It is a detection technology worthy of promotion. .
Experimental part
※ Model 722E visible spectrophotometer. NH4Cl (excellent pure), anhydrous Na2CO3, sodium tetraborate, sodium potassium tartrate, CuSO4, manganese sulfate, CaCl2, MgSO4, KH2PO4, NaCl, K2SO4, NaNO3, NaNO2, ZnSO4, AgNO3, salicylic acid; Sodium nitroferrocyanide and ammonium ferrous sulfate are of analytical grade.
※ Sodium dichloroisocyanurate (NaDCC) has an effective chlorine content of 60%.
※Ammonia nitrogen standard stock solution (Ï = 1000 mg /L) : Weigh 3. 8190 g NH4Cl (NH4Cl, excellent grade, dried at 100-105 °C for 2 h) Dissolve in water, transfer to 1 000 mL volumetric flask, dilute To the marking line. This solution is stable for 1 month.
※Ammonia nitrogen standard intermediate solution (Ï = 100 mg /L): Pipette 10. 0 mL of ammonia nitrogen standard stock solution in a 100 mL volumetric flask and dilute to the mark. This solution is stable for 1 week.
※Ammonia nitrogen standard use solution (Ï = 1. 0 mg /L): Pipette 1.0 mL of ammonia nitrogen standard stock solution into a 100 mL volumetric flask and dilute to the mark.
※Ammonia nitrogen solid detection reagent: mixing reagent salicylic acid, sodium nitroferricyanide, NaDCC, borax, sodium carbonate with a certain mass ratio (0. 5: 1. 0: 0. 05: 2. 5: 25) Ammonia nitrogen solid detection reagent is obtained.
The 0. 0,0. 1,0. 2,0. 5,1,3,5,10 mL in a 10 mL colorimetric tube, diluted with water to the engraved line, formulated to 0. 0 ~ 1. 0 mg / L ammonia nitrogen standard solution. Add a suitable amount of solid reagent by adding ammonia nitrogen, shake it, and react for color after a certain period of time. Using the reagent blank as a reference, the absorbance was measured at 696 nm using a 1 cm cuvette and made 3 parallels.
results and analysis
Selection of reaction conditions
1. The color development time is selected by selecting 0.5 mg / L ammonia nitrogen standard solution, adding ammonia nitrogen to detect the solid reagent, and measuring the absorbance at 25 ° C for 5, 10, 30, 60, 120 min. The results showed that the absorbance value of the reaction solution gradually increased with time, and the reaction remained unchanged after 10 min. The absorbance value was maintained at 0. 495 ±0. 005, and the absorbance value remained unchanged within 120 min. Therefore, the color development time is selected for 10 min.
2, 0. 5, 10. 0,7. 0,8. 5, 10. 8, 11. 6, 12. 0, 12. 5 0. 5 mg /L The ammonia nitrogen standard solution was 10 mL each, and the solid reagent was mixed with ammonia nitrogen to be mixed, and reacted at 25 ° C for 10 min, and the absorbance was measured after color development. The result shows that when the pH of the water sample is between 3. 0 and 11.6, the absorbance value reaches a maximum value and is maintained at 0.50 ± 0. 005; when pH < 3. 0 or pH > 11 At 6 o'clock, the absorbance value decreases rapidly.至之间。 The pH of the water sample is between 3. 0 ~ 11. 6 between.
3, the effect of temperature selection 0. 5 mg / L ammonia nitrogen standard solution, add ammonia nitrogen test solid reagent mixing, respectively, at 5 ° C, 10 ° C, 20 ° C, 25 ° C, 30 ° C, 35 ° C, 40 ° C conditions 10 Min, colorimetric determination of its absorbance value. The results show that the absorbance of the ammonia-nitrogen reaction solution increases with the temperature rise below 25 °C. When the temperature is between 25 °C and 35 °C, the absorbance remains basically unchanged. When the temperature is higher than 35 °C, the absorbance is higher. It tends to decrease with increasing temperature, so the reaction temperature is preferably between 25 ° C and 35 ° C during the measurement.
in conclusion
The ammonia nitrogen is used to detect solid reagents, and the detection of ammonia nitrogen is quick, simple, accurate and reliable. Compared with other methods for rapidly detecting ammonia nitrogen in water by using solid reagents, the method utilizes sodium carbonate-borax buffering reagent instead of sodium hydroxide, which solves the disadvantage that sodium hydroxide is easily deliquescent in air and improves the pH measurement used in the method. The range, if used in conjunction with a colorimeter, can be used for rapid detection of ammonia nitrogen in a variety of water environments.
At present, the ammonia nitrogen determination method is sensitive to low temperature, which may be caused by a slowdown of the chemical reaction rate in the water at a low temperature, which may result in a low measurement result. It has been proved by further experiments that the reagent reaction time is prolonged at a temperature lower than 25 ° C. By 30 minutes, the effects of low temperatures can be eliminated.
Item number
CAS
product name
package
characteristic
Market price¥
C16-S10761
6132-02-1
Sodium carbonate
500g
Shishui, AR
31
C16-M10905
119-36-8
Methyl salicylate
500ml
CP, 98%
62
C16-P11405
10043-35-3
Boric acid PH standard substance
10g
pH standard value: 9.18
599
C16-S10580
13755-38-9
Sodium nitroferricyanide
25g
ACS
96
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