Ammonia (measured in N) -Nesser reagent spectrophotometry
Minimum detection mass concentration
The minimum detection mass of this method is 1.0μg ammonia (N), if 50mL water sample determination, the minimum detection mass concentration is 0.02 mg/L.
The common calcium, magnesium and iron plasma in water can precipitate during the determination process, which can be masked by adding potassium and sodium tartrate. The residual chlorine in the water sample is combined with ammonia to form chloramines, which can be dechlorinated by sodium thiosulfate. The suspended matter in the water can be removed by coagulation precipitation of zinc sulfate and sodium hydroxide.
Sulfides, copper, aldehydes and so on can also cause turbidity of the solution. Fatty amines, aromatic amines, ferrous, etc., can produce color with mercuric potassium iodide. Colored substances in water can also cause interference. In this case, it can be removed by distillation.
The common calcium, magnesium and iron plasma in water can precipitate during the determination process, which can be masked by adding potassium and sodium tartrate. The residual chlorine in the water sample is combined with ammonia to form chloramines, which can be dechlorinated by sodium thiosulfate. The suspended matter in the water can be removed by coagulation precipitation of zinc sulfate and sodium hydroxide.
Sulfides, copper, aldehydes and so on can also cause turbidity of the solution. Fatty amines, aromatic amines, ferrous, etc., can produce color with mercuric potassium iodide. Colored substances in water can also cause interference. In this case, it can be removed by distillation.
Principles
Ammonia in water forms a yellow to brown compound (NH2Hg2OI) under alkaline conditions with Nessler’s reagent (K2Hgl4), whose coloration is proportional to the ammonia content.
Reagent (Warning: mercury iodide is highly toxic!)
All reagents for this method must be prepared in pure water without ammonia. Ammonia-free water can be prepared by ordinary pure water through strong acid type cation exchange resin or by redistillation after adding sulfuric acid and potassium permanganate.
Sodium thiosulfate solution (3.5g/L): Weigh 0.35g sodium thiosulfate pentahydrate (Na2S2O3·5H2O) and dissolve in pure water, and dilute to 100mL. This 0.4mL solution can remove the residual chlorine of 1mg/L in 200mL water sample. The amount of added can be calculated according to the mass concentration of residual chlorine in the water sample when using.
Sodium tetraborate solution (9.5g/L): Weigh 9.5g sodium tetraborate decahydrate (Na2B4O7·10H2O) and dissolve it with pure water, and dilute it to 1 000mL.
Sodium hydroxide solution (4g/L).
Borate buffer solution: Measure 88mL sodium hydroxide solution (4g/L) and dilute it to 1 000mL with sodium tetraborate solution (9.5g/L).
Boric acid solution (20g/L).
Zinc sulfate solution (100g/L): Weigh 10g zinc sulfate heptahydrate (ZnSO4·7H₂O), dissolve in a small amount of pure water, and dilute to 100mL.
Sodium hydroxide solution (240g/L).
Potassium sodium tartrate solution (500g/L): Weigh 50g potassium sodium tartrate tetrahydrate (KNaC4H4O6·4H2O) and dissolve in 100ml. In pure water, heat and boil until there is no ammonia, cool and then supplement with pure water to 100 mL.
Sodium hydroxide solution (320g/L).
NAT’s reagent: Weigh 100g mercury iodide (HgI2) and 70g potassium iodide (KI), dissolve in a small amount of pure water, pour the solution slowly into the cooled 500mL sodium hydroxide solution (320g/L), do not stop stirring, and then dilute to 1000mL with pure water. Store in a brown bottle, tightly sealed with rubber stopper, away from light.
Note: Nessler’s reagent and Nessler’s reagent. Be careful not to excess potassium iodide when preparing the reagent. Excessive iodide ions will affect the formation of colored complexes, resulting in lower results. The sodium reagent stored for a long time should be colored with a known amount of ammonia (N) standard solution before use, and the absorbance should be checked; No turbidity occurs within 2h after adding the reagent, otherwise reformulate.
Ammonia (N) standard reserve solution [ρ(NH3-N)=1.00 mg/mL]: Put ammonium chloride (NH4Cl) in the oven, bake at 105 ℃ for 1h, weigh 3.8190g after cooling, dissolve in pure water in a volumetric bottle to 1000mL, or use certified reference material solution.
Ammonia (measured in N) standard use solution [ρ(NH3-N)=10,00μg/mL]: Absorb 10.00mL ammonia (measured in N) standard reserve solution, with pure water fixed volume to 1000mL, now used.
Sodium thiosulfate solution (3.5g/L): Weigh 0.35g sodium thiosulfate pentahydrate (Na2S2O3·5H2O) and dissolve in pure water, and dilute to 100mL. This 0.4mL solution can remove the residual chlorine of 1mg/L in 200mL water sample. The amount of added can be calculated according to the mass concentration of residual chlorine in the water sample when using.
Sodium tetraborate solution (9.5g/L): Weigh 9.5g sodium tetraborate decahydrate (Na2B4O7·10H2O) and dissolve it with pure water, and dilute it to 1 000mL.
Sodium hydroxide solution (4g/L).
Borate buffer solution: Measure 88mL sodium hydroxide solution (4g/L) and dilute it to 1 000mL with sodium tetraborate solution (9.5g/L).
Boric acid solution (20g/L).
Zinc sulfate solution (100g/L): Weigh 10g zinc sulfate heptahydrate (ZnSO4·7H₂O), dissolve in a small amount of pure water, and dilute to 100mL.
Sodium hydroxide solution (240g/L).
Potassium sodium tartrate solution (500g/L): Weigh 50g potassium sodium tartrate tetrahydrate (KNaC4H4O6·4H2O) and dissolve in 100ml. In pure water, heat and boil until there is no ammonia, cool and then supplement with pure water to 100 mL.
Sodium hydroxide solution (320g/L).
NAT’s reagent: Weigh 100g mercury iodide (HgI2) and 70g potassium iodide (KI), dissolve in a small amount of pure water, pour the solution slowly into the cooled 500mL sodium hydroxide solution (320g/L), do not stop stirring, and then dilute to 1000mL with pure water. Store in a brown bottle, tightly sealed with rubber stopper, away from light.
Note: Nessler’s reagent and Nessler’s reagent. Be careful not to excess potassium iodide when preparing the reagent. Excessive iodide ions will affect the formation of colored complexes, resulting in lower results. The sodium reagent stored for a long time should be colored with a known amount of ammonia (N) standard solution before use, and the absorbance should be checked; No turbidity occurs within 2h after adding the reagent, otherwise reformulate.
Ammonia (N) standard reserve solution [ρ(NH3-N)=1.00 mg/mL]: Put ammonium chloride (NH4Cl) in the oven, bake at 105 ℃ for 1h, weigh 3.8190g after cooling, dissolve in pure water in a volumetric bottle to 1000mL, or use certified reference material solution.
Ammonia (measured in N) standard use solution [ρ(NH3-N)=10,00μg/mL]: Absorb 10.00mL ammonia (measured in N) standard reserve solution, with pure water fixed volume to 1000mL, now used.
Instrument and equipment
Spectrophotometer (V-1300PC)
All-glass still :500mL.
Colorimetric tube with stopper :50mL.
All-glass still :500mL.
Colorimetric tube with stopper :50mL.
Preservation of water sample
Ammonia in water sample is unstable, add 0.8mL sulfuric acid (ρ20=1.84 mg/L) per liter of water sample during sampling, refrigerate and store at 0 ℃~4℃, and analyze as soon as possible.
Pretreatment of water sample
Clear and colorless water samples can be directly determined. Water samples with higher chroma, turbidity and more interfering substances need to go through pretreatment steps such as distillation or coagulation precipitation.
Distillation: 200mL pure water is taken into an all-glass still, 5mL borate buffer solution and several glass beads are added, and heated and distilled until no ammonia can be detected by Nassler reagent in the distillate. After slightly cooling, pour out and discard the residual liquid in the distillation bottle, measure 200mL water sample (or take appropriate amount, dilute to 200mL with pure water) in the distillation bottle, calculate and add appropriate amount of sodium thiosulfate solution (3.5g/L) to dechlorinate according to the residual chlorine content in the water. Adjust the water sample with sodium hydroxide solution (4g/L) to be neutral.
Distillation: 200mL pure water is taken into an all-glass still, 5mL borate buffer solution and several glass beads are added, and heated and distilled until no ammonia can be detected by Nassler reagent in the distillate. After slightly cooling, pour out and discard the residual liquid in the distillation bottle, measure 200mL water sample (or take appropriate amount, dilute to 200mL with pure water) in the distillation bottle, calculate and add appropriate amount of sodium thiosulfate solution (3.5g/L) to dechlorinate according to the residual chlorine content in the water. Adjust the water sample with sodium hydroxide solution (4g/L) to be neutral.
Experimental procedure
Add 5mL of borate buffer solution and heat to distill. Use a 200mL volumetric bottle as the receiving bottle and fill 20mL boric acid solution (20g/L) as the absorption solution. The condensing tube end of the still should be inserted into the absorbent solution. When about 150mL has been steamed, leave the condensing tube end away from the liquid level and continue distilling to clean the condensing tube. Finally dilute to the scale with pure water and shake well for color comparison.
Coagulation and precipitation: Take 200mL water sample, add 2mL zinc sulfate solution (100g/L), mix well. Add 0.8mL~1mL sodium hydroxide solution (240g/L), make the pH value 10.5, let it stand for a few minutes, pour out the supernatant for colorimetric use. The water samples precipitated by zinc sulfate and sodium hydroxide can generally be clarified after standing, and can be centrifuged if necessary. If it is necessary to filter, attention should be paid to the contamination of the water sample by the ammonium salt in the filter paper. In advance, the filter paper should be washed repeatedly with pure water without ammonia, until no ammonia can be detected by Nesser’s reagent before use.
Take 50.0mL of clarified water sample or pre-treated water sample [if the content of ammonia (N) is greater than 0.1mg, then take appropriate water sample and add pure
Water to 50mL] in a 50mL colorimetric tube.
Take another 8 50mL colorimetric tubes and add them into the standard solution 0mL, 0.10mL, 0.20mL, 0.30mL, 0.50mL, 0.70mL, 0.90mL and 1.20mL of ammonia (as N). For the standard series of ammonia (as N) with high quality concentration, add the standard solution 0mL, 0.90ml and 1.20ml respectively. 0.50mL, 1.00mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL and 10.00mL, diluted to 50mL with pure water.
Add 1mL potassium and sodium tartrate solution (240g/L) into the water sample and the standard solution tube respectively (the pre-distilled water sample, this reagent is not added to the water sample and the standard tube), mix well, add 1.0mL of Nassler’s reagent and place for 10min, and use 1cm colorimetric dish at the wavelength of 420nm with pure water as the reference to determine the absorbance; If the ammonia (N) content is less than 30μg, use a 3cm colorimetric dish, less than 10μg can be used for visual colorimetric. Note: For the water sample treated by distillation, only add 5mL boric acid solution (20g/L) to each standard tube, and then add 2mL of Nahler’s reagent to each water sample and standard tube.
Draw the standard curve, from the curve to find out the content of ammonia (N) in the sample tube, or visual colorimetric record the quality of the water sample equivalent to ammonia (N) standard.
Coagulation and precipitation: Take 200mL water sample, add 2mL zinc sulfate solution (100g/L), mix well. Add 0.8mL~1mL sodium hydroxide solution (240g/L), make the pH value 10.5, let it stand for a few minutes, pour out the supernatant for colorimetric use. The water samples precipitated by zinc sulfate and sodium hydroxide can generally be clarified after standing, and can be centrifuged if necessary. If it is necessary to filter, attention should be paid to the contamination of the water sample by the ammonium salt in the filter paper. In advance, the filter paper should be washed repeatedly with pure water without ammonia, until no ammonia can be detected by Nesser’s reagent before use.
Take 50.0mL of clarified water sample or pre-treated water sample [if the content of ammonia (N) is greater than 0.1mg, then take appropriate water sample and add pure
Water to 50mL] in a 50mL colorimetric tube.
Take another 8 50mL colorimetric tubes and add them into the standard solution 0mL, 0.10mL, 0.20mL, 0.30mL, 0.50mL, 0.70mL, 0.90mL and 1.20mL of ammonia (as N). For the standard series of ammonia (as N) with high quality concentration, add the standard solution 0mL, 0.90ml and 1.20ml respectively. 0.50mL, 1.00mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL and 10.00mL, diluted to 50mL with pure water.
Add 1mL potassium and sodium tartrate solution (240g/L) into the water sample and the standard solution tube respectively (the pre-distilled water sample, this reagent is not added to the water sample and the standard tube), mix well, add 1.0mL of Nassler’s reagent and place for 10min, and use 1cm colorimetric dish at the wavelength of 420nm with pure water as the reference to determine the absorbance; If the ammonia (N) content is less than 30μg, use a 3cm colorimetric dish, less than 10μg can be used for visual colorimetric. Note: For the water sample treated by distillation, only add 5mL boric acid solution (20g/L) to each standard tube, and then add 2mL of Nahler’s reagent to each water sample and standard tube.
Draw the standard curve, from the curve to find out the content of ammonia (N) in the sample tube, or visual colorimetric record the quality of the water sample equivalent to ammonia (N) standard.
Test data processing
Calculate the mass concentration of ammonia (N) in the water sample according to the formula:
Rho (NH3 – N) = mV
ρ(NH3-N)- The mass concentration of ammonia (in N) in the water sample, in milligrams per liter (mg/L);
m- the mass of ammonia (in N) in the sample tube, measured from the standard curve, in micrograms (μg);
V– the volume of the water sample in milliliters (mL).
m- the mass of ammonia (in N) in the sample tube, measured from the standard curve, in micrograms (μg);
V– the volume of the water sample in milliliters (mL).
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