Formaldehyde is a colorless gas with a strong pungent smell. Soluble in water, alcohol and ether. Formaldehyde is gaseous at room temperature and usually exists in the form of aqueous solution. 35 ~ 40% aqueous formaldehyde solution is called formalin. Phenolic resin (bakelite) can be formed by condensation polymerization of aldehyde groups in formaldehyde molecules.

This instrument collects air samples from the test site. Formaldehyde in the air is absorbed by phenol reagent solution to generate azine, which is oxidized by trivalent iron ions in acidic solution to generate blue-green compounds. According to the color depth, direct colorimetric determination is carried out on the spot.

Because the detection value of indoor pollution has a great relationship with the temperature, humidity and air pressure of the detection environment, according to normal detection, the detection value often deviates from the expected value.