Method 1. Barium sulfate turbidimetric method
Minimum detection mass concentration
The minimum detection mass of this method is 0.25mg. If 50mL water sample is taken for determination, the minimum detection mass concentration is 5mg/mL.
This method is suitable for the determination of sulfate mass concentration less than 40mg/L water sample. Stirring speed, time, temperature and reagent addition method can affect the determination results of barium sulfate turbidimetric method, so it is required to strictly control the consistency of operating conditions.
This method is suitable for the determination of sulfate mass concentration less than 40mg/L water sample. Stirring speed, time, temperature and reagent addition method can affect the determination results of barium sulfate turbidimetric method, so it is required to strictly control the consistency of operating conditions.
Principle
Sulfate and barium ions in water form barium sulfate precipitates, forming turbidity, the degree of turbidity is proportional to the sulfate content in the water sample.
reagent
① Sulfate standard solution [ ρ(SO42-) = 1mg/mL]: Weigh 1.4786g anhydrous sodium sulfate (Na2SO4) or 1.8141g anhydrous potassium sulfate (K2SO4), dissolve in pure water, and fixed volume to 1000mL, or use certified standard material.
② Stabilizer solution: weigh 75gsodium chloride (NaCl),dissolve in 300mL pure water, add 30mL hydrochloric acid ( ρ20 = 1.19g /mL), 50 ml. Glycerin (C3H8O2) and 100mL ethanol [φ (C2H5OH)=95%], mixed well.
③ Barium chloride dihydrate crystal (BaCl2·2H2O), the particle size of 20 mesh to 30 mesh.
② Stabilizer solution: weigh 75gsodium chloride (NaCl),dissolve in 300mL pure water, add 30mL hydrochloric acid ( ρ20 = 1.19g /mL), 50 ml. Glycerin (C3H8O2) and 100mL ethanol [φ (C2H5OH)=95%], mixed well.
③ Barium chloride dihydrate crystal (BaCl2·2H2O), the particle size of 20 mesh to 30 mesh.
Instrument and equipment
① Electromagnetic stirrer
②V-1500PC spectrophotometer
②V-1500PC spectrophotometer
Experimental steps
① Absorb 50mL water sample into 100mL beaker, if the mass concentration of sulfate in the water sample exceeds 40mg/L, take appropriate water sample and dilute it to 50mL;
② Add 2.5mL stabilizer solution, adjust the speed of the electromagnetic stirrer, so that the solution does not splash out during agitation, and can dissolve 0.2g barium chloride crystal (BaCI2 ·2H2O) in 10 s to 30s. Fixed this condition, in the same batch of determination should not be changed;
③ Take 6 100mL beakers of the same type, and add the sulfate standard solution [ ρ(SO) = 1mg/mL] 0mL, 0.25 mL, 0.50 mL, 1.00 mL, 1.50 mL and 2.00mL, respectively. Add pure water to 50mL each. Make the mass concentrations 0mg/L, 5.0 mg/L, 10.0 mg/L, 20.0 mg/L, 30.0mg/L, and 40.0mg/L(in SO42-), respectively;
④ Take another 50ml water sample, under the same conditions as the standard series, add 2.5mL stabilizer solution to the water sample and the standard series respectively, and add 0.2g barium chloride dihydrate crystal (BaCI2 ·2H2O) when the stirring rate is stable, and time it immediately, stirring for 60 s±5 s. Each beaker was timed from the addition of barium chloride crystal to the exact 10min at a wavelength of 420 nm and a 3cm colorimetric dish, using pure water as the reference to measure light absorption;
⑤ Draw the working curve, and the quality of sulfate in the sample can be found on the curve.
② Add 2.5mL stabilizer solution, adjust the speed of the electromagnetic stirrer, so that the solution does not splash out during agitation, and can dissolve 0.2g barium chloride crystal (BaCI2 ·2H2O) in 10 s to 30s. Fixed this condition, in the same batch of determination should not be changed;
③ Take 6 100mL beakers of the same type, and add the sulfate standard solution [ ρ(SO) = 1mg/mL] 0mL, 0.25 mL, 0.50 mL, 1.00 mL, 1.50 mL and 2.00mL, respectively. Add pure water to 50mL each. Make the mass concentrations 0mg/L, 5.0 mg/L, 10.0 mg/L, 20.0 mg/L, 30.0mg/L, and 40.0mg/L(in SO42-), respectively;
④ Take another 50ml water sample, under the same conditions as the standard series, add 2.5mL stabilizer solution to the water sample and the standard series respectively, and add 0.2g barium chloride dihydrate crystal (BaCI2 ·2H2O) when the stirring rate is stable, and time it immediately, stirring for 60 s±5 s. Each beaker was timed from the addition of barium chloride crystal to the exact 10min at a wavelength of 420 nm and a 3cm colorimetric dish, using pure water as the reference to measure light absorption;
⑤ Draw the working curve, and the quality of sulfate in the sample can be found on the curve.
Experimental data processing
To calculate the mass concentration of sulfate (SO42-) in the water sample;
ρ(SO42-) = mV×1000
ρ(SO42-) — mass concentration of sulfate (measured as SO42-) in water sample, in milligrams per liter (mg/L);
m — the mass of sulfate in the sample from the working curve, in milligrams (mg);
V — volume of water sample, in milliliters (mL).
m — the mass of sulfate in the sample from the working curve, in milligrams (mg);
V — volume of water sample, in milliliters (mL).
Method 2: Barium chromate spectrophotometry (thermal method)
Minimum detection mass concentration
The minimum detection mass of this method is 0.25mg. If 50mL water sample is taken for determination, the minimum detection mass concentration is 5mg/L.
This method is suitable for the determination of sulfate mass concentration less than 200mg/L water sample. The carbonate in the water sample can form precipitation interference with barium ion, but the interference can be eliminated by adding acid and boiling.
This method is suitable for the determination of sulfate mass concentration less than 200mg/L water sample. The carbonate in the water sample can form precipitation interference with barium ion, but the interference can be eliminated by adding acid and boiling.
Principle
In an acidic solution, barium chromate forms barium sulfate precipitates and chromate ions with sulfate. After neutralizing the solution, filter to remove the excess barium chromate and the resulting barium sulfate, filtrate.
That is, chromic acid ion replaced by sulfate, showing yellow, colorimetric quantification.
That is, chromic acid ion replaced by sulfate, showing yellow, colorimetric quantification.
reagent
① Sulfate standard solution [ ρ(SO42-) = 1mg/mL]: Weigh 1.4786g anhydrous sodium sulfate (Na2SO4) or 1.8141g anhydrous potassium sulfate (K2SO4), dissolve in pure water, and fixed volume to 1000mL, or use certified standard material.
② Barium chromate suspension: weigh 19.44g potassium chromate (K2CrO4) and 24.44g barium oxydihydrate (BaCl2 ·2H2O), dissolve in 1000mL pure water, heat to boiling. Mix the two solutions in a 3000mL beaker. Allow the resulting yellow barium chromate to precipitate. When the precipitation has decreased, pour out the supernatant. Wash the precipitation 5 times with 1000mL of pure water by pouring method each time. Add pure water to 1000mL to make a suspension. Mix well before each use. Note: About 48mg of sulfate can be precipitated per 5mL of suspension.
③ Ammonia (1+1): Take ammonia ( ρ20=0.88g/mL) and pure water equal volume mix.
④ Hydrochloric acid solution [c(HCI)=2.5 mol/L]: Take 208mL hydrochloric acid ( ρ20=1.19g/mL), add pure water and dilute to 1000mL.
② Barium chromate suspension: weigh 19.44g potassium chromate (K2CrO4) and 24.44g barium oxydihydrate (BaCl2 ·2H2O), dissolve in 1000mL pure water, heat to boiling. Mix the two solutions in a 3000mL beaker. Allow the resulting yellow barium chromate to precipitate. When the precipitation has decreased, pour out the supernatant. Wash the precipitation 5 times with 1000mL of pure water by pouring method each time. Add pure water to 1000mL to make a suspension. Mix well before each use. Note: About 48mg of sulfate can be precipitated per 5mL of suspension.
③ Ammonia (1+1): Take ammonia ( ρ20=0.88g/mL) and pure water equal volume mix.
④ Hydrochloric acid solution [c(HCI)=2.5 mol/L]: Take 208mL hydrochloric acid ( ρ20=1.19g/mL), add pure water and dilute to 1000mL.
Instrument and equipment
①V-1500PC spectrophotometer;
② colorimetric tube with stopper :50mL and 25mL.
② colorimetric tube with stopper :50mL and 25mL.
Experimental steps
① Take 50.0mL water sample and put it in 150mL conical bottle; Note: the glass instrument used in this method is not treated with potassium dichromate sulfuric acid lotion. In order to prevent the influence of contamination in the test, the conical bottle is treated with hydrochloric acid solution (1+1) before use and washed with tap water or pure water.
② Take another 8 150mL conical bottles, add 0mL, 0.25 mL, 0.50 mL, 1.00 mL, 3.00 mL, 5.00 mL, 7.00 mL and 10.00mL sulfate standard solution [ ρ(SO42-) = 1mg/mL], and add pure water to 50.0mL each. The mass concentrations of sulfate were 0mg/L, 5 mg/L, 10 mg/L, 20 mg/L, 60 mg/L, 100 mg/L, 140 mg/L and 200mg/L(calculated by SO42-), respectively;
③ Add 1mL hydrochloric acid solution [c(HCl)= 2.5mol /L] to the water sample and the standard series solution, heat and boil for about 5min, so as to decompose and remove the interference of carbonate. Add 2.5mL barium chromate suspension and boil for about 5min (the volume of the solution is about 25 mL).
④ Takeoff the conical bottle and add ammonia (1+1) to each bottle drop by drop until the liquid is lemon yellow, then add 2 drops.
⑤ After cooling, transfer to 50mL stopper colorimetric tube, add pure water to the scale, shake well.
⑥ Filter the above solution through the dry slow speed quantitative filter paper. Discard the first 5mL of filtrate. Collect the filtrate in a dry 25ml colorimetric tube. At 420nm, the absorbance was measured in a 0.5cm colorimetric dish with pure water as the reference. Note: For 440nm wavelength, 1em colorimetric m is used. For sulphate series lower than 4mg, 3cm colorimetric dish is used.
⑦ Draw a working curve and find out the quality of sulfate in the sample tube from the curve.
② Take another 8 150mL conical bottles, add 0mL, 0.25 mL, 0.50 mL, 1.00 mL, 3.00 mL, 5.00 mL, 7.00 mL and 10.00mL sulfate standard solution [ ρ(SO42-) = 1mg/mL], and add pure water to 50.0mL each. The mass concentrations of sulfate were 0mg/L, 5 mg/L, 10 mg/L, 20 mg/L, 60 mg/L, 100 mg/L, 140 mg/L and 200mg/L(calculated by SO42-), respectively;
③ Add 1mL hydrochloric acid solution [c(HCl)= 2.5mol /L] to the water sample and the standard series solution, heat and boil for about 5min, so as to decompose and remove the interference of carbonate. Add 2.5mL barium chromate suspension and boil for about 5min (the volume of the solution is about 25 mL).
④ Takeoff the conical bottle and add ammonia (1+1) to each bottle drop by drop until the liquid is lemon yellow, then add 2 drops.
⑤ After cooling, transfer to 50mL stopper colorimetric tube, add pure water to the scale, shake well.
⑥ Filter the above solution through the dry slow speed quantitative filter paper. Discard the first 5mL of filtrate. Collect the filtrate in a dry 25ml colorimetric tube. At 420nm, the absorbance was measured in a 0.5cm colorimetric dish with pure water as the reference. Note: For 440nm wavelength, 1em colorimetric m is used. For sulphate series lower than 4mg, 3cm colorimetric dish is used.
⑦ Draw a working curve and find out the quality of sulfate in the sample tube from the curve.
Test data processing
According to the mass concentration of sulfate (SO42-) in the calculated water sample;
ρ(SO42-) = mV×1000
ρ(SO42-) — mass concentration of sulfate (measured as SO42-) in water sample, in milligrams per liter (mg/L);
m — the mass of sulfate in the sample from the working curve, in milligrams (mg);
V — volume of water sample, in milliliters (mL).
m — the mass of sulfate in the sample from the working curve, in milligrams (mg);
V — volume of water sample, in milliliters (mL).
Method 3: Barium chromate Spectrophotometry ( cold method)
Minimum detection mass concentration
The minimum detection mass of this method is 0.05mg, if 10mL water sample is taken for determination, the minimum detection mass concentration is 5mg/L;
This method is suitable for the determination of sulfate mass concentration less than 100mg/L water sample. The carbonate in the water sample can form precipitation interference with barium ion, but the interference can be eliminated by adding acid and boiling.
This method is suitable for the determination of sulfate mass concentration less than 100mg/L water sample. The carbonate in the water sample can form precipitation interference with barium ion, but the interference can be eliminated by adding acid and boiling.
Principle
In an acidic solution, barium chromate forms barium sulfate precipitates and chromate ions with sulfate. Ethanol is added to reduce the solubility of barium chromate in the aqueous solution, and the barium sulfate is filtered out.
Excessive barium chromate precipitation, the filtrate is replaced by sulfate chromate ions, showing yellow, colorimetric quantification.
Excessive barium chromate precipitation, the filtrate is replaced by sulfate chromate ions, showing yellow, colorimetric quantification.
reagent
① Sulfate standard solution [ ρ(SO42-) = 0.5mg/mL]: accurately weigh 0.9071g potassium sulfate (K2SO4) dried at 105℃. Dissolve in pure water, and dilute the constant volume to 1000mL, or use certified reference material.
② Barium chromate suspension: Weigh 2.5g barium chromate (B aCrO3), add 200ml acetic acid-hydrochloric acid mixture {[c(CH3COOH)=1 mol/L] and [c(HCI)=0.02 mol/L] equal volume mixture}, shake and mix fully to make suspension, store in polyethylene bottle, shake well before use.
③ Calcium chloride-ammonia solution: Weigh 1.9g calcium chloride dihydrate (CaCl2·2H2O), dissolve in 500mL ammonia water [c(NH3 ·H2O)=6 mol/L], dense storage.
④ Ethanol [φ(C2H5OH)=95%].
② Barium chromate suspension: Weigh 2.5g barium chromate (B aCrO3), add 200ml acetic acid-hydrochloric acid mixture {[c(CH3COOH)=1 mol/L] and [c(HCI)=0.02 mol/L] equal volume mixture}, shake and mix fully to make suspension, store in polyethylene bottle, shake well before use.
③ Calcium chloride-ammonia solution: Weigh 1.9g calcium chloride dihydrate (CaCl2·2H2O), dissolve in 500mL ammonia water [c(NH3 ·H2O)=6 mol/L], dense storage.
④ Ethanol [φ(C2H5OH)=95%].
Instruments and equipment
①V-1500PC spectrophotometer;
② colorimetric tube with stopper :50mL and 25mL.
② colorimetric tube with stopper :50mL and 25mL.
Experimental steps
① Absorb 10.0mL. Water sample and place it in 25mL. Colorimetric tube
② Take 8 25mL colorimetric tubes with stopper and add 0mL, 0.10mL, 0.20mL, 0.40mL, 0.60mL, 0.80mL and 1.00 respectively mL and 2.00mL sulfate standard solution [ ρ(SO42-) =
0.5mg/mL] were added with pure water to 10.0mL, The sulfate mass concentrations were 0mg/L, 5 mg/L, 10 mg/L, 20 mg/L, 30 mg/L, 40mg/L, 50mg/L and 100mg/L(calculated by SO42-), respectively;
③ Add 5.0mL of fully shaken barium chromate suspension into the water sample and standard pipe, mix thoroughly, and let stand for 3min.
④ Add 1.0mL calcium chlorine-ammonia solution, mix well, add 10ml. Ethanol [φ(C2H5OH)=95%], plug, shake violently for 1 min.
⑤ Filter with slow quantitative filter paper, discard 10mL of initial filtrate, collect filtrate in 10mL stopper colorimetric tube, in 420nm wavelength,3cm colorimetric dish, using pure water as reference, measurement of absorbance.
⑥ To subtract the absorbance corresponding to the quality of sulfate after the blank, draw a working curve, and find out the quality of sulfate in the sample tube from the curve.
② Take 8 25mL colorimetric tubes with stopper and add 0mL, 0.10mL, 0.20mL, 0.40mL, 0.60mL, 0.80mL and 1.00 respectively mL and 2.00mL sulfate standard solution [ ρ(SO42-) =
0.5mg/mL] were added with pure water to 10.0mL, The sulfate mass concentrations were 0mg/L, 5 mg/L, 10 mg/L, 20 mg/L, 30 mg/L, 40mg/L, 50mg/L and 100mg/L(calculated by SO42-), respectively;
③ Add 5.0mL of fully shaken barium chromate suspension into the water sample and standard pipe, mix thoroughly, and let stand for 3min.
④ Add 1.0mL calcium chlorine-ammonia solution, mix well, add 10ml. Ethanol [φ(C2H5OH)=95%], plug, shake violently for 1 min.
⑤ Filter with slow quantitative filter paper, discard 10mL of initial filtrate, collect filtrate in 10mL stopper colorimetric tube, in 420nm wavelength,3cm colorimetric dish, using pure water as reference, measurement of absorbance.
⑥ To subtract the absorbance corresponding to the quality of sulfate after the blank, draw a working curve, and find out the quality of sulfate in the sample tube from the curve.
Test data processing
According to the mass concentration of sulfate (SO42-) in the calculated water sample;
ρ(SO42-) = mV×1000
ρ(SO42-) – Mass concentration of sulfate (measured as SO42-) in water sample, in mg/L;
m — the mass of sulfate in the sample from the working curve, in milligrams (mg);
V — volume of water sample, in milliliters (mL).
m — the mass of sulfate in the sample from the working curve, in milligrams (mg);
V — volume of water sample, in milliliters (mL).
The Difference
Sulfate is one of the important indicators for routine monitoring of drinking water quality. There are generally the following methods for the detection of sulfate in water: gravimetric method, ion chromatography, atomic absorption method, turbidimetric method of sulfuric acid, spectrophotometry of chariot acid chin [2]. With the rapid development of instrument analysis science and technology, foreign scholars believe that flame atomic absorption method and ion chromatography have better results in detecting sulfate content in water, but their operation steps are more complicated and can not be used in the laboratory.
In terms of method 1 and method 2, through the comparison of the accuracy, accuracy and average recovery of the two methods, the results show that the relative error of method 1 is 3.07%, and the recovery rate is 98.9%~102.4%; The relative error of method 2 is 2.09%, and the recovery rate is 99.6%~104.7%; There was no statistical difference between the two methods for the determination of sulfate content. The sulfate in water was detected by the method of hydrazine spectrophotometry with better precision and accuracy. The lowest detection mass concentration of method 3 is lower and suitable for the detection of lower concentration.
In terms of method 1 and method 2, through the comparison of the accuracy, accuracy and average recovery of the two methods, the results show that the relative error of method 1 is 3.07%, and the recovery rate is 98.9%~102.4%; The relative error of method 2 is 2.09%, and the recovery rate is 99.6%~104.7%; There was no statistical difference between the two methods for the determination of sulfate content. The sulfate in water was detected by the method of hydrazine spectrophotometry with better precision and accuracy. The lowest detection mass concentration of method 3 is lower and suitable for the detection of lower concentration.
Scheme basis: GB/T 5750.5-2023
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