Journalist/Editor Li Li/Photographer Chen Yongjie/Checked by Zhang Xinghai/Li Yunfeng

This article is compiled by China Digital Science and Technology Museum in conjunction with Beijing Science and Technology Daily, Science and Technology Life Weekly

Recently, an article entitled "Ali P7 employee died of leukemia and rented a free formaldehyde room before his death" has aroused heated debate. Many people begin to pay attention to the air quality of houses, and are keen to buy formaldehyde self testing boxes or formaldehyde detectors to measure the formaldehyde content of houses.

At present, the so-called "artifact" that can detect formaldehyde on the market is roughly divided into two categories: formaldehyde self testing box and formaldehyde detector. The price of formaldehyde self-test box is relatively cheap, and the basic price is below 10 yuan. There are many kinds of formaldehyde detectors, and the price difference is large, ranging from dozens of yuan to tens of thousands of yuan.

So are these so-called convenient and fast household formaldehyde detection artifacts really reliable? Is the detected data reliable? What method does the professional authoritative testing organization use to detect formaldehyde? Next, let the reporter of Beijing Science and Technology News take you to the Beijing Physical and Chemical Testing Center and tell you with experiments.

● Time: September 10th

● Location: Gu'an Experimental Base of Beijing Physical and Chemical Testing Center

● Purpose: Test whether the formaldehyde data obtained from 8 household formaldehyde detection products are accurate

● Principle: The common detection principle of formaldehyde meter on the market is divided into electrochemical method and colorimetric method

● Experimental guidance: Dr. You Hui

● Sample: 5 formaldehyde test strips and 3 electronic formaldehyde detectors (all purchased from a self run store on an e-commerce platform)

● Main experimental instruments: 30 cubic meter experimental bin, gaseous pollutant generator, ppm formaldehyde detector, constant flow sampler, ultraviolet visible spectrophotometer, etc. The overall structure of the test chamber is mainly composed of the cabin, air mixing fan system, air circulation system, exhaust system (including air valve), air inlet system (including air valve), sampling and filling ports (2), operation ports, etc.

30m3 laboratory cabin

Constant current sampler

Ultraviolet visible spectrophotometer

● Reference standards: According to GB/T18883-2002 Indoor Air Quality Standard, the safety limit of formaldehyde concentration is 0.1mg/m3

Experimental steps

1. 8 formaldehyde test products are numbered randomly, the formaldehyde test box serial number is 1-5, and the formaldehyde detector serial number is 6-8

2. Open the white absorption boxes in the five formaldehyde detection boxes respectively, and pour the white powder (absorbent) into the absorption boxes, and then pour the liquid (deionized water) into the white vials; Open and calibrate the formaldehyde detector No. 6-8

▲ The tester is ready to pour the white powder (absorbent) into the white round absorption box

3. Put the formaldehyde test products 1-8 and the thermometer and hygrometer into the 30m3 standard experimental chamber, close the door of the experimental chamber, and start the mixing fan and circulating fan

4. When the temperature and humidity are stable, inject formaldehyde gas into the experimental chamber, and use the ppm formaldehyde detector to measure the concentration of formaldehyde in the chamber in real time. When the formaldehyde concentration reaches 0.36mg/m3, the mixing fan will work for another 20 minutes to make the formaldehyde mixing more uniform and then close, and the circulating fan will remain open throughout the process

▲ The experimenter is operating and starting the gaseous pollutant generator (silver box) to release formaldehyde

▲ The experimenter is using the ppm formaldehyde detector to measure the formaldehyde concentration in the warehouse in real time

5. Read the data displayed on the 6-8 formaldehyde detector

6. (Sampling process of professional testing instrument) Connect the constant flow sampler to the sampling port of the experimental chamber, use a large bubble absorption tube with 5mL absorption liquid inside, collect 10L gas at a flow rate of 0.5L/min, and record the temperature and atmospheric pressure of the sampling point. After sampling, pour the absorption solution into a color developing bottle and take it back to the laboratory, then measure the absorbance with a spectrophotometer at 630nm, and analyze the formaldehyde concentration in the air

▲ Dr. You Hui is preparing formaldehyde absorption solution

▲ Dr. You Hui uses an instrument to measure the formaldehyde concentration in the warehouse in real time

7. After sampling, open the large air volume ventilation fan at the bottom of the equipment to exhaust the formaldehyde gas in the test chamber

8. When the concentration of formaldehyde in the experimental chamber recovers to the concentration before detection, open the chamber door, take out the formaldehyde test box 1-5, pour the liquid (developer) in the brown bottle into the white absorption box, compare the color with the color card, and record the value

Experimental data: (Click the picture to zoom in)



Experiment conclusion: The detection data error of formaldehyde test box and formaldehyde tester is too large, which is of little significance for reference. It is suggested to use professional spectrophotometer method to detect formaldehyde concentration.

Note: The experimental data only represent the test results under the experimental environment at that time.

Experimental analysis:

Which principle is used for formaldehyde detection box? Why not?

You Hui: Formaldehyde detection boxes are basically based on the colorimetric principle, which is to use a specific liquid to absorb formaldehyde and other substances to change color, and then compare the color change with the standard colorimetric card to get the test results. It belongs to semi quantitative detection with strong subjectivity and low accuracy. The light, temperature and humidity of the environment, the observer's operation method, observation angle, color sensitivity, etc. will affect the result reading. The reliability of the results of the formaldehyde test box used by ordinary consumers at home is poor. For example, the formaldehyde concentration of 0.1mg/m3 and 0.2mg/m3 on the color card of the detection box is not much different, but the former is up to standard, while the latter is twice as high.

What principle does the household formaldehyde detector use? Why not?

You Hui: The formaldehyde test instrument using electrochemical method has an electrochemical sensor, which is composed of two metal electrical levels and electrolytes. The formaldehyde gas molecule undergoes redox reaction under the electrode voltage, producing a current signal whose size is proportional to the formaldehyde concentration in the air. The signal is amplified and digitally processed to display the formaldehyde concentration. Some will use integrated circuits to ensure the reliability of data.

At present, there are two kinds of portable detectors on the market: semiconductor detector and electrochemical detector. However, regardless of the type, the air flow rate, humidity and temperature will have a great impact on the accuracy of the data.

In fact, we still lack unified technical standards for such products. Our country does not stipulate what kind of certification the civilian portable detector needs to pass before it is listed again, and it is not a measuring instrument.

What kind of formaldehyde detection method is used by professional organizations?

You Hui: Phenol reagent spectrophotometry is used in the national standard GB/T18204.26-2000 Determination of Formaldehyde in the Air of Public Places. The principle is that formaldehyde in the indoor air reacts with phenol reagent to form a zine, which is oxidized by high iron ions in acid solution to form a blue-green compound. It is quantified by colorimetry according to the color depth. Phenol reagent absorption solution shall be prepared before sample collection. The air sampler is used to collect samples from the indoor detection points of the target building.

What kind of organization is more reliable for formaldehyde detection?

You Hui: Professional testing institutions have professional and comprehensive equipment and technicians, which can digitize indoor air pollutant indicators such as formaldehyde, which is more intuitive and accurate. Generally speaking, a formal testing organization will have a CMA certificate (China Metrology Certification), and the CMA mark will also be used in the test report.

What is the source of harmful substances in the air?

Youhui: First, indoor pollution, building materials, decoration materials (such as synthetic fiber, artificial floor, white latex, paint, paint, plastic, thermal insulation and sound insulation materials); Second, unqualified decorative textiles, wallpaper, carpets, curtains, furniture, bedding, etc; Third, unqualified kitchen utensils, detergents, pesticides, printing inks, preservatives, etc. can release a certain amount of formaldehyde, toluene and other harmful substances. In addition, industrial exhaust gas, automobile exhaust gas and dust from outdoor will also flow into the room with the flow of air.

How to remove formaldehyde in a newly decorated house?

You Hui: The best and safest way is natural ventilation. Under normal circumstances, the ventilation is more than half a year, and the volatile gas content in the newly decorated house can basically reach the standard. Formaldehyde is closely related to the selection of decoration materials. If the formaldehyde exceeds the standard too much, the ventilation is difficult to reach the standard. If formaldehyde is contained in the plate, its basic release time is more than ten years, or even longer. Generally, formaldehyde exceeding the standard of boards is because formaldehyde is compressed in the materials used, and its release is also very slow. The formaldehyde contained in textile products such as curtains can be cleaned. Because formaldehyde is soluble in water, water washing can simply remove formaldehyde. Therefore, the key is to optimize the living environment from the source.

If the house formaldehyde exceeds the standard, is there any treatment plan?

You Hui: At present, the treatment scheme of professional institutions is roughly divided into physical adsorption and chemical reaction to consume formaldehyde in the air. At present, there are two kinds of formaldehyde scavengers on the market. One is to purify the air by neutralizing formaldehyde and generating harmless substances; The other is to purify the air by sealing formaldehyde to prevent its volatilization.

Why are there two different national standards for formaldehyde detection?

One is Indoor Air Quality Standard (GB/T18883-2002). The standard was issued by the General Administration of Quality Supervision, Inspection and Quarantine, the Ministry of Health and the State Environmental Protection Administration on December 19, 2002 and implemented on March 1, 2003. The safety limit of formaldehyde concentration specified in this standard is 0.1mg/m3, which is a recommended standard but not a mandatory standard. This standard is applicable to housing and buildings. It is the minimum standard for the health of a residential environment and the fundamental basis for measuring whether a house is environmentally friendly.

Second, Code for Indoor Environmental Pollution Control of Civil Buildings GB50325-2010. This standard was jointly issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China and the Ministry of Construction in 2001, implemented in 2002 and revised in 2006, 2010 and 2013. Note: Class I buildings: residential buildings, hospitals, elderly buildings, kindergartens, school classrooms, etc. Class II buildings: office buildings, shops, hotels, cultural and entertainment places, libraries, gymnasiums, and public places.

The difference between the two standards lies in: first, the nature of the standards is different. GB50325 is a mandatory standard issued by the Ministry of Construction, which is mainly applicable to the completion acceptance inspection of public facilities and civil facilities such as residential buildings, office buildings, stations, etc. It is required to test 1 month after the completion of the project. GB/T 18883 is a recommended national standard issued by the State Environmental Protection Administration and the Ministry of Health. It is a guiding standard.

Second, the two standard determination methods and time are different. The index measurement time of GB50325 is one hour after closing the doors and windows, and that of GB/T 18883 is 12 hours after closing the doors and windows. After the doors and windows are closed, the indoor air and outdoor air cannot convection. The longer the closing time is, the higher the temperature is, the higher the concentration of pollutants accumulated in the room is. Therefore, it is often measured by GB50325 that it does not exceed the standard, and GB/T 18883 does.

Third, the standard test items are different. GB50325 is five test items, while GB/T18883 is more than 20 test items. GB50325 is the standard for project acceptance. GB/T18883 is actually closer to people's daily life habits, because people usually spend more than 8 hours in their homes. The measured results are actually more accurate, with the purpose of ensuring people's health.

Qizhu (Beijing ） Technology Development Co., Ltd. also contributed to this article