Measurement of formaldehyde and ammonia in indoor air

Summary

Formaldehyde is a colorless, irritating and water-soluble gas that binds to proteins. Inhalation of high concentrations of formaldehyde can cause severe irritation and edema of the respiratory tract, eye stinging, headache, and bronchial asthma can also occur. Direct skin contact with formaldehyde can cause dermatitis, discoloration, necrosis. Frequent inhalation of small amounts of formaldehyde can cause chronic poisoning, mucosal congestion, skin irritation, allergic dermatitis, keratinized and brittle nails, and pain at the fingertips of nail beds.

Operation method

Formaldehyde-phenol reagent colorimetric method; Ammonia-naphthol reagent colorimetric method

Principle

Formaldehyde and ammonia in the sample to be measured react with a coloring agent to produce colored compounds with selective absorption of visible light and the establishment of the colorimetric analysis method. Formaldehyde reacts with phenol reagent to produce blue-green compounds, and ammonia reacts with Nano reagent to produce yellow compounds, and the color of the compounds is directly proportional to the content of formaldehyde and ammonia, which are measured at a wavelength of 430 nm.

Materials and Instruments

Air
Deionized water Distilled water Solid formaldehyde reagent Liquid formaldehyde reagent Ammonia reagent
Formaldehyde, ammonia meter

Move

I. Determination of formaldehyde
1. Pre-sampling preparations

Connect the absorbent bottle to the buffer bottle and the buffer bottle to the air sampler air inlet with rubber tubing and place on a tripod. Add 10 mL of deionized water and a formaldehyde reagent (I) to the white A colorimetric bottle, stopper tightly and shake for 10 s to dissolve completely. At the same time, add the same water and reagent to the blue B colorimetric flask for blanking and zeroing.
2. Sampling

Transfer the solution in the White A colorimetric vial to the bubble absorber tube, insert the mill plug into the bubble absorber tube and secure it with a rubber band to prevent air leakage. Turn on the switch of the atmospheric sampler, adjust the sampling time to 10 min and the gas flow rate to 0.5 liter/min, and start sampling. Record the temperature and atmospheric pressure at the time of sampling.
3. Pre-test preparation

At the end of sampling, remove the bubble absorber tube, transfer all the solution to the white A colorimetric flask, dilute it with water to the scale, stopper it tightly and shake it well, then heat the white A and blue B colorimetric flasks close to the body temperature for 7 min. Then add 1 formaldehyde reagent (II) to the white A and blue B colorimetric flasks, stopper it tightly and shake it well and heat it close to the body temperature for 5 min to develop the color. Remove the cap and screw the colorimetric positioner onto the colorimetric vials and wait for measurement.
4. Testing

Turn on the power switch of the colorimeter, press the selection key, move the cursor to A formaldehyde and press the confirmation key. Put the blue B colorimetric vial into the colorimetric bath, press the zero key to adjust zero, remove the blue A colorimetric vial, put the white A colorimetric vial into the colorimetric bath, and then press the direct reading key to directly read the absorbance and concentration value (mg/L).
II. Determination of ammonia
1. Pre-sampling preparations

Connect the absorption bottle to the buffer bottle and the buffer bottle to the air sampler air inlet with rubber tubing and place on a tripod. Take 1 ammonia reagent (I) and put all drops into the white B colorimetric bottle, add deionized water to the 10 mL mark, close the stopper, and shake for 10 s to make the mixture homogeneous. At the same time, add the same volume of water and reagent into the blue B colorimetric flask for blank adjustment.
2. Sampling

Transfer the solution in the white B colorimetric flask to the bubble absorber tube, insert the mill plug into the bubble absorber tube and fix it with a rubber band to prevent air leakage. Turn on the switch of the atmospheric sampler, adjust the sampling time to 10-20 min and the gas flow rate to 0.5-1.0 liter/min, and start sampling. Record the temperature and atmospheric pressure at the time of sampling.
3. Pre-test preparation

At the end of sampling, remove the bubble absorber tube and transfer all the solution to the white B colorimetric flask, dilute with water to the scale and shake well with a tight stopper. Then add 1 ammonia reagent (II) to the white B and blue A colorimetric bottles respectively, stopper tightly and shake well. Remove the cap and screw the colorimetric positioner onto the colorimetric flask and leave for measurement.
4. Testing

Turn on the power switch of the colorimeter, press the selection key, move the cursor to B ammonia and press the confirmation key. Put the blue B colorimetric vial into the colorimetric bath, press Zero key to adjust zero, remove the blue A colorimetric vial, put the white A colorimetric vial into the colorimetric bath, and then press Direct Reading key to directly read the absorbance and concentration value (mg/L).
III. Calculation of results
1. Calculation of the concentration of formaldehyde (ammonia) in air at different temperatures at one atmospheric pressureC=C0×10/V0 , V0=Vt×273/(273+T)Eq:C - formaldehyde (ammonia) concentration in air, ^mg/m3;C0 - formaldehyde (ammonia) meter display value. mg/L;10 - volume of the solution in the colorimetric flask at the time of measurement, mL;V0 - volume of the sample in standard condition (20°C, one atmosphere), L;T - air temperature at the sampling point, °C.
2. Calculation of formaldehyde (ammonia) concentration in air at different temperatures and atmospheric pressuresC=C0×10/V0, V0=Vt×﹝273/(273+T﹞×P/101.3Eq:P - atmospheric pressure at the sampling point, KPa. others as above.

Caveat

1. close windows and doors for 12 hours prior to sampling, and close windows and doors during sampling.

2. less than 50 m21-3 points should be set up in rooms smaller than 50 m2 ; 50-100 m2 ; 1-3 points should be set up in rooms smaller than 50 m2 .

2. 1 to 3 points should be set up in rooms less than 50 m2 ; 50 to 100 m23 to 5 points should be set up in rooms less than 50 m2 ; 50 to 100 m2 ; 100 m2At least 5 points should be set up above 100 m2 , evenly distributed on the diagonal or in a plum blossom pattern.

3. The sampling height should be consistent with the height of the human respiratory zone. The relative height should be between 0.5 and 1.5 meters.

4. The relative deviation should not exceed 20% for each parallel sampling. Relative deviation = (measured value - average value) 100~H average value.

5. Formaldehyde reagent and ammonia reagent must be protected from light and stored at low temperature 4℃.

Common Problems

I. Introduction

Formaldehyde is a colorless, irritating and water-soluble gas that binds to proteins. After inhalation of high concentration of formaldehyde, severe irritation and edema of the respiratory tract, eye stinging, headache, bronchial asthma can also occur. Direct skin contact with formaldehyde can cause dermatitis, discoloration, necrosis. Frequent inhalation of small amounts of formaldehyde can cause chronic poisoning, mucosal congestion, skin irritation, allergic dermatitis, keratinized and brittle nails, nail bed fingertip pain. Formaldehyde in the indoor environment mainly from the pollution of outdoor air (industrial exhaust, automobile exhaust, photochemical smog, etc. to a certain extent can be emitted or produced a certain amount of formaldehyde) and indoor decoration materials pollution. General newly renovated house formaldehyde content can reach 0.40 ^mg/m3, individual may reach 1.50 ^mg/m3. Ammonia is very soluble in water, on the eyes, throat, upper respiratory tract, the role of fast, irritating, light cause congestion and secretion increase, and then can cause pulmonary edema. Prolonged exposure to low concentrations of ammonia can cause laryngitis, hoarseness. Ammonia in indoor air, mainly from the concrete admixtures used in building construction, but also from the interior decorative materials, such as furniture painted with additives and whitening agents used in most of the ammonia. Generally speaking, ammonia pollution release period is relatively fast, will not accumulate in the air for a long time, the harm to the human body is relatively small, but it should also cause everyone's attention.

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