HJ 601-2011Water quality. Determination of formaldehyde. Acetylacetone spectrophotometric method (English PDF)

Foreword

To protect the environment and protect the human body in order to implement the Environmental Protection Law of the People's Republic of China and the Law of the People's Republic of China on Water Pollution Prevention and Control to develop and standardize the monitoring methods for formaldehyde in water.

The method for determining formaldehyde in surface water, groundwater and industrial wastewater is specified in this standard.

This standard is a revision of the "Method for the determination of formaldehyde in water quality by acetylacetone spectrophotometry" (GB 13197-91).

This standard was first published in 1991, and the original standard drafting unit was the Beijing Environmental Protection Monitoring Center. This is the first revision. the Lord the content to be revised is as follows.

- the scope of application increases groundwater;

-- Revise the color development conditions;

-- Revise the calculation formula;

-- Increase quality assurance and quality control.

The national environmental protection standard "Water quality approved and issued by the former National Environmental Protection Agency on August 31, 1991 since the implementation of this standard.

Determination of formaldehyde acetylacetone spectrophotometry (GB 13197-91) abolished.

This standard was formulated by the Science and Technology Standards Department of the Ministry of Environmental Protection.

This standard is mainly drafted by. China Shipbuilding Industry Corporation, the 718th Research Institute.

This standard was approved by the Ministry of Environmental Protection on February 10, 2011.

This standard has been implemented since June 1, 2011.

This standard is explained by the Ministry of Environmental Protection.

Water quality - Determination of formaldehyde - Acetylacetone spectrophotometric method

1 Scope of application

This standard specifies the acetylacetone spectrophotometric method for the determination of formaldehyde in water.

This standard applies to the determination of formaldehyde in surface water, groundwater and industrial wastewater. This standard does not apply to printing and dyeing wastewater.

When the sample volume is 25 ml and the cuvette has an optical path length of 10 mm, the method detection limit is 0.05 mg/L, and the measurement range is 0.20 to 3.20 mg/L.

2 Principle of the method

Formaldehyde forms a yellow compound with acetylacetone in the presence of an excess of ammonium salt, which has maximum absorption at 414 nm.

The absorbance of the colored substance was basically unchanged within 3 h.

The chemical reaction formula is.

H NH3 2 (CH3 C

C CH2

CH3)

CCH3 CH2

CH2 C

CH3 3H2O

3 Interference and elimination

The concentration of acetaldehyde in the water sample is less than 3 mg/L, and the propionaldehyde, butyraldehyde, acrolein, etc. are less than 5 mg/L, respectively, and do not interfere with the determination. Also when Methanol was 20 mg/L, phenol was 50 mg/L, and no interference was observed when free cyanide was 1 mg/L.

4 Reagents and materials

Unless otherwise stated in this standard, the reagents used should be analytically pure reagents that meet national or professional standards. The experimental water is distilled water.

Or water of the same purity.

4.1 Sulfuric acid. rho(H2SO4) = 1.84 g/ml.

4.2 Sodium hydroxide. c (NaOH) = 1 mol/L.

Weigh 110 g of sodium hydroxide, dissolve in 100 ml of water, shake well, transfer to a polyethylene container, and place in a sealed container until the solution is clear. Measure 54 ml of the supernatant, diluted to 1 000 ml with water, and mixed.

4.3 Sulfuric acid solution. c(1/2 H2SO4) = 1 mol/L.

Measure 30 ml of sulfuric acid (4.1), slowly inject into 1000 ml of water, cool and mix.

4.4 Sulfuric acid solution. c (1/2 H2SO4) = 6 mol/L.

Measure 180 ml of sulfuric acid (4.1), slowly inject into 850 ml of water, cool and mix.

4.5 Iodine solution. c (1/2I2) ~ 0.05 mol/L.

Weigh 6.35 g of pure iodine and 20 g of potassium iodide, first dissolve in a small amount of water, then dilute to 1 000 ml with water. Iodine solution should be stored in the stopper the brown bottle is placed in the dark.

4.6 Acetylacetone solution.

Dissolve 50 g of ammonium acetate (CH3COONH4), 6 ml of glacial acetic acid (CH3COOH) and 0.5 ml of acetylacetone (C5H8O2) in 100 ml of water. This solution was stored at 4 ° C for stable storage for one month.

Note. The purity of acetylacetone has an effect on the absorbance of the blank test. Acetylacetone should be colorless and transparent, and if necessary, it should be refined by distillation.

4.7 Potassium dichromate reference solution. c (1/6K2Cr2O7) = 0.050 0 mol/L.

Accurately weigh 2.451 6 g of reference potassium dichromate baked at 110-130 ° C for 2 h and cooled to room temperature. Dissolve in water and transfer to 1 000 ml.

In a volumetric flask, dilute to the mark with water and shake well.

4.8 Starch indicator. rho = 10 g/L.

Weigh 1 g of starch, add 5 ml of water to make a paste, add the paste to 90 ml of boiling water with stirring, and boil for 1 to 2 minutes.

Cool and dilute to 100 ml. Available now.

4.9 Sodium thiosulfate standard solution. c (Na2S2O3 · 5H2O) ~ 0.05 mol/L.

Weigh 12.5 g of sodium thiosulfate dissolved in boiled and cooled water and dilute to 1 000 ml. Add 0.4 g of sodium hydroxide and store in brown the inside of the color bottle was placed for 2 weeks, filtered, and calibrated with a potassium dichromate reference solution (4.7) before use. The calibration method is as follows.

Add about 1 g of potassium iodide (KI) and 50 ml of water to a 250 ml iodine bottle, and add 20.00 ml of potassium dichromate reference solution (4.7).

Add 5 ml of sulfuric acid solution (4.4), mix and place in the dark for 5 min. Titrate with sodium thiosulfate solution, until titrated until the solution is light yellow at the time, add 1 ml of starch indicator (4.8), continue titration until the blue color just fades, and record the amount (V1).

The concentration of sodium thiosulfate standard solution is calculated by formula (1).

C1 = 2 2

Where. c1--sodium thiosulfate standard solution concentration, mol/L;

C2--potassium dichromate reference solution concentration, mol/L;

V1--titration consumption volume of sodium thiosulfate solution, ml;

V2--take the potassium dichromate reference solution volume, ml.

4.10 Formaldehyde standard stock solution. (HCHO)rho ~1 mg/ml.

Preparation. Pipette 2.8 ml of formaldehyde reagent (formaldehyde content 36% ~ 38%), dilute with water to 1 000 ml, shake. Prepared solution Store at 4 ° C for half a year. Pre-calibration before use.

Calibration. Pipette 20.00 ml of formaldehyde standard stock solution into 250 ml iodine flask, add 50.0 ml iodine solution (4.5), add 15 ml Mix the sodium hydroxide solution (4.2) and let stand for 15 min. Add 20 ml of sulfuric acid solution (4.3), mix and let stand for 15 min. Thiosulfuric acid Sodium standard solution (4.9) is titrated. When the solution is light yellow, add 1 ml of starch indicator (4.8) and continue to titrate to blue.

Faded, write down the amount (V).

At the same time, accurately remove 20.00 ml of water instead of formaldehyde standard stock solution. Carry out the blank test in the same way, and record the sodium thiosulfate standard.

Quasi-solution dosage (V0).

The mass concentration of formaldehyde standard stock solution is calculated by formula (2).

(HCHO)rho = 0 1( ) 15.02 1 000 20.00 VV c- × × × (2) where. (HCHO)rho-formaldehyde standard stock solution concentration, mg/ml;

V0--blank test consumption of sodium thiosulfate standard solution volume, ml;

V--calibration of formaldehyde storage liquid consumption of sodium thiosulfate standard solution volume, ml;

C1--sodium thiosulfate standard solution concentration, mol/L;

15.02--molar mass of formaldehyde (1/2HCHO), g/mol;

1 000--1 g is equal to 1 000 mg;

20.00--Move the volume of formaldehyde standard stock solution, ml.

Note 1. The starch solution should be added at the near end of the titration.

Note 2. The titration should be carried out in an iodometric flask and should be protected from sunlight. The titration should not be excessively shaken.

5 Instruments and equipment

Unless otherwise indicated, the gauges used in this standard shall be Class A glass gauges in accordance with national standards.

5.1 Full glass distiller 500 ml.

5.2 25 ml with a colorimetric tube.

5.3 Constant temperature water bath.

5.4 Spectrophotometer.

5.5 Common instruments used in general laboratories.

6 Samples

7 Analysis steps

8 Calculation of results

The formaldehyde mass concentration rho in the sample is calculated according to formula (4).

rho = (4)

Where. rho--the mass concentration of formaldehyde in the sample, mg/L;

W--the amount of formaldehyde calculated from the calibration curve (7.1.4) or calculated using equation (3), µg;

V--the volume of the sample, ml.

9 Precision and accuracy

Seven laboratories measured three uniform water samples at different levels of concentration, with formaldehyde levels of 0.35, 1.15, and 11.4 mg/L, respectively.

10 Quality Assurance and Quality Control