Water quality-Determination of total phosphorus-
Ammonium molybdate spectrophotometric method
GB 11893-89
Approval date 1989-09-01 Implementation date 1991-09-01
1 Subject content and scope of application
This standard stipulates This method uses potassium persulfate (or nitric acid-perchloric acid) as the oxidant to digest unfiltered water samples, and uses ammonium molybdate spectrophotometry to determine total phosphorus.
Total phosphorus includes dissolved, particulate, organic and inorganic phosphorus.
This standard applies to surface water, sewage and industrial wastewater.
Take 25mL of sample, the minimum detection concentration of this standard is 0.01mg/L, and the upper limit of determination is 0.6mg/L.
Under acidic conditions, arsenic, chromium, and sulfur interfere with the determination.
2 Principle
Use potassium persulfate (or nitric acid-perchloric acid) to digest the sample under neutral conditions, and oxidize all the phosphorus contained into orthophosphate. In acidic media, orthophosphate reacts with ammonium molybdate to form phosphomolybdate heteropoly acid in the presence of antimony salt, which is immediately reduced by ascorbic acid to form a blue complex.
3 Reagents
Unless otherwise stated, the reagents used in this standard should use analytical reagents that comply with national standards or professional standards and distilled water or water of equivalent purity.
3.1 Sulfuric acid (H2SO4), density is 1.84g/mL.
3.2 Nitric acid (HNO3), density is 1.4g/mL.
3.3 Perchloric acid (HClO4), excellent grade pure, density is 1.68g/mL.
3.4 Sulfuric acid (H2SO4), 1:1.
3.5 Sulfuric acid, about c(1/2H2SO4)=1mo1/L: Add 27mL sulfuric acid (3.1) to 973mL water.
3.6 Sodium hydroxide (NaOH), 1mo1/L solution: Dissolve 40g sodium hydroxide in water and dilute to 1000mL.
3.7 Sodium hydroxide (NaOH), 6mo1/L solution; dissolve 240g sodium hydroxide in water and dilute to 1000mL.
3.8 Potassium persulfate, 50g/L solution: Dissolve 5g of potassium persulfate (K2S2O8) in dry water and dilute to 100mL.
3.9 Ascorbic acid, 100g/L solution: Dissolve 10g ascorbic acid (C6H8O6) in water and dilute to 100mL.
This solution is stored in a brown reagent bottle and is stable for several weeks in a cold place. It can be used for a long time if it does not discolor.
3.10 Molybdate solution: Dissolve 13g of ammonium molybdate [(NH4)6Mo7O24?4H2O] in 100mL of water. Dissolve 0.35g potassium antimony tartrate [KSbC4H4O7? 1 H2O] in 100mL water. Slowly add the ammonium molybdate solution to 300 mL of sulfuric acid (3.4) under constant stirring, add potassium antimony tartrate solution and mix evenly.
This solution is stored in a brown reagent bottle and can be stored in a cold place for two months.
3.11 Turbidity-color compensation solution: Mix two volumes of sulfuric acid (3.4) and one volume of ascorbic acid solution (3.9). Prepare on the day of use.
3.12 Phosphorus standard stock solution: Weigh 0.2197±0.001g of potassium dihydrogen phosphate (KH2PO4) that was dried at 110°C for 2 hours and cooled in a desiccator. Dissolve it in water and transfer it to a 1000mL volumetric flask. Add About 800mL water, add 5mL sulfuric acid (3.4), dilute with water to the mark and mix well. 1.00mL of this standard solution contains 50.0μg phosphorus.
This solution can be stored in glass bottles for at least six months.
3.13 Phosphorus standard solution: Transfer 10.0mL of phosphorus standard solution (3.12) into a 250mL volumetric flask, dilute to the mark with water and mix well. 1.00mL of this standard solution contains 2.0μg of phosphorus.
Prepare on the day of use.
3.14 Phenolphthalein, 10g/L solution: 0.5g phenolphthalein dissolved in 50mL95% ethanol.
4 Instruments
Commonly used laboratory instruments and equipment and the following instruments.
4.1 Medical portable steam sterilizer or general pressure cooker (1.1~1.4kg/cm2).
4.2 50mL stoppered (ground) graduated tube.
4.3 Spectrophotometer.
Note: All glassware should be soaked in dilute hydrochloric acid or dilute nitric acid.
5 Sampling and Samples
5.1 Take 500mL of water sample and add 1mL of sulfuric acid (3.1) to adjust the pH value of the sample to less than or equal to 1, or do not add any reagent to the sample. Store in cold place.
Note: For water samples with low phosphorus content, do not use plastic bottles for sampling, as phosphates are easily adsorbed on the walls of plastic bottles.
5.2 Preparation of sample:
Take 25mL sample (5.1) into a stoppered graduated tube (4.2). When taking it, shake it carefully to obtain a sample that is representative of both the dissolved and suspended parts. If the phosphorus concentration in the sample is high, the sample volume can be reduced.
6 Analysis steps
6.1 Blank sample
Carry out a blank test according to the provisions of (6.2), replace the sample with water, and add the same volume as when measuring reagents.
6.2 Determination
6.2.1 Digestion
6.2.1.1 Potassium persulfate digestion: Add 4mL potassium persulfate (3.8) to the sample (5.2) , after plugging the cover of the graduated tube tightly, use a small piece of cloth and thread to tie the glass plug tightly (or fix it with other methods), place it in a large beaker and place it in a high-pressure steam sterilizer (4.1) for heating. When the pressure reaches 1.1kg/cm2 and the corresponding temperature is 120℃, stop heating after maintaining it for 30 minutes. After the pressure gauge reading drops to zero, take it out and let it cool. Then dilute with water to the mark.
Note: If water samples are preserved with sulfuric acid. When digesting with potassium persulfate, the sample needs to be adjusted to neutrality first.
6.2.1.2 Nitric acid-perchloric acid digestion: Take 25mL sample (5.1) in an Erlenmeyer flask, add a few glass beads, add 2mL nitric acid (3.2), heat on the electric hot plate and concentrate to 10mL . After cooling, add 5mL of nitric acid (3.2), then heat and concentrate to 10mL, and let cool. Add 3 mL of perchloric acid (3.3) and heat until the perchloric acid emits white smoke. At this time, you can add a small funnel to the Erlenmeyer flask or adjust the temperature of the electric hot plate to keep the digestion liquid in the reflux state on the inner wall of the Erlenmeyer flask until 3 ~4mL, let cool.
Add 10mL of water and 1 drop of phenolphthalein indicator (3.14). Add sodium hydroxide solution (3.6 or 3.7) dropwise until it just turns reddish, then add sulfuric acid solution (3.5) dropwise until the reddish color just fades, and mix thoroughly. Transfer to a stoppered graduated tube (4.2) and dilute with water to the mark.
Note: ① Digestion with nitric acid-perchloric acid needs to be carried out in a fume hood. The mixture of perchloric acid and organic matter is prone to danger when heated. The sample needs to be digested with nitric acid first, and then nitric acid-perchloric acid is added for digestion.
② Never steam the digested sample to dryness.
③If there is residue after digestion, filter it with filter paper into a graduated tube with a stopper, and thoroughly clean the Erlenmeyer flask and filter paper with water
and move them to the graduated tube with a stopper. in the tube.
④ When the organic matter in the water sample cannot be completely destroyed by potassium persulfate oxidation, this method can be used to digest it.
6.2.2 Color development
Add 1mL of ascorbic acid solution (3.9) to each digestion solution and mix thoroughly. After 30 seconds, add 2mL molybdate solution (3.10) and mix thoroughly. .
Note: ① If the sample contains turbidity or chromaticity, a blank sample needs to be prepared (diluted with water to the mark after digestion) and then
added to the sample Add 3 mL of turbidity-color compensation solution (3.11), but do not add ascorbic acid solution and molybdate solution. Then
subtract the absorbance of the blank sample from the absorbance of the sample.
② If arsenic is greater than 2 mg/L and interferes with the determination, use sodium thiosulfate to remove it. If sulfide is greater than 2mg/L and interferes with the determination, it should be removed by nitrogen gas. Chromium greater than 50mg/L interferes with the determination and should be removed with sodium sulfite.
6.2.3 Spectrophotometric measurement
After leaving it at room temperature for 15 minutes, use a cuvette with a light path of 30mm and measure the absorbance at a wavelength of 700nm using water as a reference. After deducting the absorbance of the blank test, check the phosphorus content from the working curve (6.2.4).
Note: If the room temperature is lower than 13℃ during color development, the color can be developed on water spray at 20~30℃ for 15 minutes.
6.2.4 Drawing of working curve
Take 7 stopper graduated tubes (4.2) and add 0.0, 0.50, 1.00, 3.00, 5.00, 10.0, 15.0mL phosphate standards respectively Solution (3.14). Add water to 25mL. Then proceed according to the measurement step (6.2). Using water as a reference, measure the absorbance. After subtracting the absorbance of the blank test, draw a working curve with the corresponding phosphorus content.
7 Expression of results
Total phosphorus content is expressed in C (mg/L), calculated according to the following formula:
Where: m——sample Measured phosphorus content, μg;
V——volume of sample for determination, mL.
8 Precision and Accuracy
8.1 Thirteen laboratories measured (using 6.2.1.1 digestion) a unified sample containing phosphorus of 2.06mg/L.
8.1.1 Repeatability
The relative standard deviation within the laboratory is 0.75%.
8.1.2 Reproducibility
The relative standard deviation between laboratories is 1.5%.
8.1.3 Accuracy
The relative error is +1.9%.
8.2 Six laboratories measured (using 6.2.1.2 digestion) a unified sample with a phosphorus content of 2.06mg/L.
8.2.1 Repeatability
The relative standard deviation within the laboratory is 1.4%.
8.2.2 Reproducibility
The relative standard deviation between laboratories is 1.4%.
8.2.3 Accuracy
The relative error is 1.9%.
The main components of the quality control sample are ethyl acid (NH2CH2COOH) and sodium glycerophosphate ( ).
Additional notes:
This standard is proposed by the Standards Division of the National Environmental Protection Administration.
This standard is drafted by the Beijing Environmental Monitoring Center and the Shanghai Environmental Monitoring Center.
The main drafters of this standard are Yuan Yulu and Yao Yuan.
China Environmental Monitoring Station is entrusted with the interpretation of this standard.
Water quality-Determination of total nitrogen-Alkaline potassium persiflage digestion-UV spectrophotometric method
Water quality-Determination of total nitrogen-Alkaline potassium persiflage digestion-UV spectrophotometric method
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GB 11894-89
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1 Subject content and scope of application
1.1 Subject content
This standard specifies the determination of total nitrogen in water using alkaline potassium persulfate digestion at 120 ~ 124°C and ultraviolet spectrophotometry method.
1.2 Scope of application
This standard is applicable to the measurement of surface water and groundwater. This method can determine the sum of nitrogen in nitrite nitrogen, ammonia nitrate, inorganic ammonium salts, dissolved ammonia and most organic nitrogen-containing compounds in water.
The minimum detectable concentration of nitrogen is 0.050mg/L, and the upper limit of determination is 4mg/L.
The molar absorption coefficient of this method is 1.47×103L·mo1-1·cm-1.
The main interferences in the measurement are iodide ions and bromide ions. The iodide ion interferes with more than 2.2 times the total nitrogen content, and the bromide ion interferes with more than 3.4 times the total nitrogen content.
Certain organic substances may have an impact on the determination if they cannot be completely converted into nitrates under the determination conditions specified in this method.
2 Definition
2.1 Total filterable nitrogen: refers to the nitrogen content of soluble and filterable solids (particulate matter less than 0.45?m) in water.
2.2 Total nitrogen: refers to the nitrogen content in soluble and suspended particles.
3 Principle
In an aqueous solution above 60℃, potassium persulfate can decompose to produce potassium bisulfate and atomic oxygen. Potassium bisulfate dissociates in the solution to produce hydrogen ions, so In the alkaline medium of sodium hydroxide, the decomposition process can be promoted to be complete.
The decomposed atomic oxygen can convert the nitrogen element of the chlorine-containing compounds in the water sample into nitrate at 120~124℃. And during this process, organic matter is oxidized and decomposed at the same time. UV spectrophotometry can be used at wavelengths of 220 and 275nm to measure the absorbance A220 and A275 respectively and calculate the corrected absorbance A according to formula (1):
A＝A220-2A275…………………… …………………………(1)
Check the calibration curve according to the value of A and calculate the total nitrogen (measured as NO3-N) content.
4 Reagents and materials
Unless otherwise stated in (4.1), analytically pure reagents that comply with national standards or professional standards will be used during analysis.
4.1 Water, no ammonia. Prepare according to one of the following methods;
4.1.1 Ion exchange method: Pass distilled water through a strong acid cation exchange resin (hydrogen type) column, and collect the effluent in a glass bottle with a sealed glass cover .
4.1.2 Distillation method: Add 0.10mL sulfuric acid (p=1.84g/mL) to 1000mL distilled water. And redistill in an all-glass still, discard the first 50 mL of distillate, and then collect the distillate in a glass bottle with a glass stopper.
4.2 Sodium hydroxide solution, 200g/L: Weigh 20m sodium hydroxide (NaOH), dissolve it in water (3.1), and dilute to 100mL.
4.3 Sodium hydroxide solution, 20g/L: obtained by diluting the (4.2) solution 10 times.
4.4 Alkaline potassium persulfate solution: Weigh 40g potassium persulfate (K2S2OB) and 15g sodium hydroxide (NaOH), dissolve in water (4.1), dilute to 1000mL, and store the solution Store in polyethylene bottles for up to one week.
4.5 Hydrochloric acid solution, 1+9.
4.6 Potassium nitrate standard solution.
4.6.1 Potassium nitrate standard stock solution, CN=100mg/L: Dry potassium nitrate (KNO3) in an oven at 105~110℃ for 3 hours. After cooling in a desiccator, weigh 0.7218g and dissolve Dissolve in water (4.1), transfer to a 1000mL volumetric flask, dilute with water (4.1) to the mark and store in a dark place at 0 to 10°C, or add 1 to 2mL of chloroform for storage. It can be stable for 6 months.
4.6.2 Potassium nitrate standard solution, CN=10mg/L: obtained by diluting the stock solution 10 times with water (4.1). Prepare when used.
4.7 Sulfuric acid solution, 1+35.
5 Instruments and Equipment
5.1 Commonly used laboratory instruments and the following instruments.
5.2 UV spectrophotometer and 10mm quartz cuvette.
5.3 Medical portable steam sterilizer or household pressure cooker (pressure is 1.1~1.4kg/cm2), the temperature in the pot is equivalent to 120~124℃.
5.4 Colorimetric tube with glass ground stopper, 25mL.
The glassware used can be soaked in hydrochloric acid (1+9) or sulfuric acid (1+35), and then rinsed several times with water (4.1).
6 Samples
6.1 Sampling
Immediately after water samples are collected, place them in a refrigerator or store them below 4°C, but not for more than 24 hours.
When the water has been left for a long time, about 0.5 mL of sulfuric acid (p=1.84g/mL) can be added to 1000 mL of water sample to acidify it to a pH less than 2 and measure it as soon as possible.
Samples can be stored in glass bottles.
6.2 Preparation of sample
Take the laboratory sample (6.1) and adjust the pH to 5~9 with sodium hydroxide solution (4.3) or sulfuric acid solution (4.7) to prepare the sample. Sample.
If the sample does not contain suspended solids, follow the step (7.1.2). If the sample contains suspended solids, follow the step (7.1.3).
7 Analysis steps
7.1 Determination
7.1.1 Use a non-grading pipette to take 10.00mL sample (when CN exceeds 100?g, the amount can be reduced Measure and add water (4.1) to dilute to 10mL) and place it in a colorimetric tube.
7.1.2 When the sample does not contain suspended matter, proceed as follows.
a. Add 5 mL of alkaline potassium persulfate solution (4.4), plug the ground stopper tightly, and tie the bottle stopper with cloth, rope, etc. to prevent it from popping out.
b. Place the colorimetric tube in a medical portable steam sterilizer and heat it until the pointer of the pressure gauge reaches 1.1~1.4kg/cm2. At this time, the timer starts when the temperature reaches 120~124℃. Or place the colorimetric tube in a household pressure cooker and heat it until the top pressure valve blows air and start timing. Keep this temperature for half an hour.
c. Cool, open the valve to release air, remove the outer cover, take out the colorimetric tube well and cool it to room temperature.
d. Add 1mL of hydrochloric acid (1+9), dilute to the 25mL mark with ammonia-free water, and mix well.
e. Pipette part of the solution to 10mm, put it into a quartz cuvette, use ammonia-free water as a reference on a UV spectrophotometer, measure the absorbance at wavelengths of 220 and 275nm, and use the formula ( 1) Calculate the corrected absorbance A.
7.1.3 When the sample contains suspended solids, first follow steps a to d in 7.1.2 above, and then transfer the supernatant to a quartz cuvette after clarification. Continue the measurement according to step e in 7.1.2 above.
7.2 Blank test
Except for replacing the test material with 10mL of water (4.1), the blank test uses exactly the same reagents, dosage and analysis steps as the measurement for parallel operation.
Note: When the measurement is close to the detection limit, the absorbance Ab of the blank test must be controlled not to exceed 0.03. If it exceeds this value, the pressure of the water, reagents, utensils and household pressure cookers or medical portable sterilizers must be checked. .
7.3 Calibration
7.3.1 Preparation of calibration series:
a. Use a graduated pipette to insert a set of (10) colorimetric tubes (5.4) , add 0.0, 0.10, 0.30, 0.50, 0.70, 1.00, 3.00, 5.00, 7.00, 10.00mL of nitrate nitrogen standard solution (4.6.2) respectively. Add water (4.1) to dilute to 10.00mL.
b. Perform the measurement according to steps a to e in 7.1.2.
7.3.2 Drawing of calibration curve:
Complete all analysis steps for the calibration series prepared from zero concentration (blank) solution and other potassium nitrate standard solutions (4.6.2). After measuring the absorbance at wavelengths of 220 and 275nm, calculate the corrected absorbance As of other calibration series except zero concentration and the corrected absorbance Ab of zero concentration and their difference Ar according to the following formulas As=As220- 2As275…………………………………………(2)
Ab＝Ab220-2Ab275………………………………………… ……(3)
Ar＝As-Ab ………………………………………………………………(4)
Where: AS220 - the absorbance of the standard solution at a wavelength of 220nm;
AS275 - the absorbance of the standard solution at a wavelength of 275nm;
Ab220 - the absorbance of the zero concentration (blank) solution at a wavelength of 220nm ;
Ab275——Absorbance of zero concentration (blank) solution at 275nm wavelength.
Draw a calibration curve based on the Ar value and the corresponding NO3-N content (micrograms).
8 Expression of results
8.1 Calculation method
Calculate the corrected absorbance Ar of the sample according to formula (1), and find the corresponding total value on the calibration curve. Nitrogen? Gram number, total nitrogen content (mg/L) is calculated according to the following formula:
In the formula: m——The measured nitrogen content of the sample, micrograms;
V—— —Volume of sample for measurement, mL.
9 Precision and Accuracy
9.1 Repeatability
21 laboratories measured sodium nitrite, aminopropionic acid and ammonium chloride mixed samples ; CW604 ammonia nitrogen standard sample; L-glutamic acid and glucose mixture. The nitrogen contents of the above three works are 1.49, 2.64 and 1.15mg/L respectively. The analysis results are as follows:
The indoor relative standard deviations of each laboratory are 2.3, 1.6 and 2.5% respectively. The allowable precision of indoor repeated measurements is 0.074, 0.092 and 0.063 mg/L respectively.
9.2 Reproducibility
The above-mentioned laboratory measured the above three unified synthetic samples. The inter-laboratory relative standard deviations were 3.1%, 1.1% and 4.2% respectively; the reproducibility relative standard deviations were 4.0%, 1.9% and 4.8% respectively; the total relative standard deviations were 3.8, 1.9 and 4.9% respectively.
9.3 Accuracy
The above-mentioned laboratory measured the above three unified synthetic samples. The relative errors of the average values ??in the laboratory were 6.3%, 2.4% and 8.7% respectively.
The indoor relative errors are 7.5%, 3.8% and 9.8% respectively. The laboratory average recovery confidence ranges were 99.0±6.4%, 99.0±5.1% and 101±9.4% respectively.
Additional notes:
This standard is proposed by the Planning and Standards Division of the National Environmental Protection Administration.
This standard is drafted by the Shanghai Environmental Monitoring Center.
The drafter of this standard is Dai Kehui.
This standard entrusts China Environmental Monitoring Station to be responsible for interpretation.