Ozone generator concentration detection method and standard

Standard: GB 28232-2011 Safety and Health Standard for Ozone Generators CJT3028.2-1994

The concentration of ozone in the use of ozone is related to the effectiveness of disinfection and sterilization, and is an important indicator of ozone generator disinfection. Nowadays, many companies control based on their own feelings, which is very unscientific. So everyone should strictly follow the national standards when using ozone generators. We need to use instruments to detect the concentration of ozone, so that we have a clear idea. If you do not know the concentration standard for ozone disinfection, you can consult a professional institution or conduct experiments to obtain the test results. The popular methods for detecting ozone concentration nowadays can be divided into three categories: physical methods, physical chemical methods, and chemical detection methods, which can be used as references for everyone.

Physical methods: The most popular method for analyzing ozone nowadays is the ultraviolet absorption method. It is an analytical instrument manufactured based on the Beer Lambert law, which utilizes the characteristic absorption of ultraviolet light at a wavelength of 254nm by ozone. As long as a suitable length of absorption cell is selected, it can detect ozone concentrations ranging from 0.002mg/m3 to 5% (vol). Its linearity is good within 4-5 orders of magnitude. This method has been adopted as the standard method for determining ozone in ambient air in China (GB1/T1154348).

The ultraviolet absorption method can not only be used to detect the concentration of ozone in gases, but also to detect the concentration of dissolved ozone in water.

The instruments for ultraviolet absorption method are available in the United States, Japan, Switzerland, and other countries. In 1985, China's Beijing Analytical Instrument Factory introduced the ML-8810 ultraviolet absorption ozone analyzer from the American company MONITORLABS for environmental testing. After 1992, the range was gradually expanded to 100ppm and 1000ppm. The Beijing Superpower Self Control Experimental Technology Research Institute developed the ZX-01 series ultraviolet absorption ozone analyzer in 1999, which has a measurement range from 0-10ppm (for environmental detection), 0-100ppm, 0-1000ppm, 0-10000ppm to 0-25000ppm.
The principle of ultraviolet absorption method: The absorption of radiation by a certain gas or liquid is controlled by Lambert Beer's law:
I=Ioe–klc
In the formula: Io - intensity of the incident light beam;
I - Intensity of the light beam passing through the sample (gas or liquid);
L - the length of the optical path through the sample;
C - concentration of absorbed substances in the sample;
K - the specific absorption coefficient of the absorbing substance at the wavelength of the light.
This type of detection requires an understanding of the k value of the substance at a known wavelength.
Ozone detection: Ozone absorbs short wave ultraviolet (200-300nm) Hartley band ultraviolet light, with the highest absorption at 253.7nm (Figure 1). At this wavelength, the range of absorption coefficient values is from 303.9 to 313.2 cm-1 · mol-1 · L (273K and 760mmHg), and researchers have confirmed that the value is 302.4 cm-1 · mol-1 · L.
The working principle of the Brown Luber analyzer (formerly Hamburg, Federal Republic of Germany) is shown in Figure 2. The radiation from the mercury lamp is focused by a condenser lens to form a parallel beam that passes through the measuring dish and illuminates the light receiver. A portion of the radiated light is refracted by the spectroscope to another light receiver used for reference detection, and the intensity is adjusted to the same level using a variable light bar. Two light receivers are connected to the bridge circuit, and the light absorbed by the measuring dish causes imbalance in the bridge circuit. A servo motor is used to restore balance, and its calibration action range is consistent with the light absorption. The instrument is equipped with automatic zero compensation. When measuring ozone in the air, inert gas is introduced into the measuring dish through an electromagnetic valve. When detecting ozone in water, standard solution is injected into the measuring dish.

Physical and chemical methods: Indigo Disulfonate Sodium (IDS) spectrophotometric method
The principle is that a gas containing ozone passes through a blue IDS solution in an absorption tube with a porous glass plate, and the generated solution is measured at 610nm using a spectrophotometer to calculate the ozone concentration. This method is relatively complex to operate and is used to detect ozone concentration in the environment or as a benchmark for calibrating physical instruments (low concentration).
The IDS method has also been designated as a national standard for determining ozone concentration in the environment (GB/T15437).
Chemiluminescence
This method utilizes excess ethylene (or NO) and ozone to produce chemiluminescence, and uses a photomultiplier tube to receive the luminescence intensity to calculate the concentration of ozone. This method was very popular in the 1970s and 1980s and was once listed as one of the environmental testing standard methods by ERP in the United States. It has now been replaced by the ultraviolet method.

Method for detecting ozone in water
In addition to iodometric and ultraviolet absorption methods, an electrochemical method called "membrane electrode" has been widely used in recent years to measure the concentration of dissolved ozone in water. It consists of a probe with a replaceable semi permeable membrane and a microprocessor. When measuring, place the sensitive part of the probe in ozone water and apply a fixed polarization voltage between the anode and cathode. The dissolved ozone passes through the semi permeable membrane to reach the cathode surface and is reduced, generating a diffusion current proportional to the concentration of ozone. The magnitude of the diffusion current can be expressed by the following equation:
I=KC
In the formula: I - diffusion current (A); K - constant; C-O3 concentration (mg/L)
After researching various semi permeable membrane materials, electrode materials, electrolytes, and applied voltage potentials abroad, a membrane electrode with steady-state voltage for current has been manufactured, which has good linearity and reproducibility. The membrane electrode method has strong anti-interference ability, high sensitivity, wide range, and can be used for online analysis and control. The trend of using membrane electrode method to analyze ozone concentration in water is becoming increasingly widespread. ATI, ROSEMENT, and ROS from Switzerland all have membrane electrode ozone analyzers.
Ozone concentration unit
In recent years, China's ozone industry has developed rapidly, with a wide variety of products. Some products express concentration in units that are confusing and easily misunderstood.
Method for expressing ozone concentration in gases
One is expressed in terms of the mass of ozone contained per unit volume, with commonly used units including mg/L, mg/m3, and μ g/m3, abbreviated as mass concentration. Their relationship is: 1mg/L=103mg/m3=106 μ g/m3
All standards in our country adopt mass concentration.
Another method of using ppm or ppb as concentration units is called volumetric concentration. Ppm (parts per million) unit refers to the volume of ozone contained in one million volumes of gas, and is commonly used as a volumetric concentration in countries such as the United States and Japan. 1ppm=103ppb
However, the meaning of ppb (parts per million) is not clear. In the United States and France, "billion" means one billion (109), and ppb means one billionth (10-9); In the UK and Germany, 'billion' is one trillion (1012), and ppb means one trillionth (10-12). Therefore, this is an easily confused expression. The Association of Pure and Applied Chemistry made a decision in July 1971 that it was not suitable for use.
In China, ppb generally refers to 10-9.
The volume concentration can also be expressed in terms of volume percentage (vol) and pphm, and their relationship is
1%（vol）=104ppm=106pphm=107ppb
Two units can be converted using the following formula:
X（ppm）=40x/3x? A（mg/m3） 或 A=3x/40x? X
In the formula: A - ozone concentration expressed in mg/m3
X - Ozone concentration expressed in ppm
M - Molar quantity of gas (ozone is 48)
22.4- Gas molar volume of NPT (standard state, 273K, 101.3KPa, i.e. 0 ℃, 760mmHg)
For example, if the ozone content in the atmosphere is 1ppm, it is expressed in mg/m3.
A=40x/3x? X=40x/3x=2.14（mg/m3）。
The standard state in the United States, Japan, and testing systems refers to a gas volume of 24.45L/mol at 298K (25 ℃) and 101.3kPa (760mmHg)
1ppm=1.963mg/m3。
There is another way to express the concentration of ozone in weight percentage. Generally expressed as% (wt), the meaning of% (wt) is: mass of ozone/mass of gas containing ozone x 100%.
In this way, under standard conditions
1ppm=2.14mg/m3=1.66×10-4%（wt）
1% (wt) (in air)=12.93g/m3=6042ppm
1% (wt) (in oxygen)=14.3g/m3=6682ppm
The air density is 1293g/m3, and the oxygen density is 1430g/m3.
Method for expressing ozone concentration in gases
The units representing dissolved ozone in water are mg/l, g/m3, and ppm (wt)
Mg/L - Its meaning is the mass of ozone (mg) divided by the volume of water containing ozone (m3)
G/m3- is the mass of ozone (mg) divided by the volume of water containing ozone (m3)
Ppm - is the mass of ozone/mass of water containing ozone multiplied by 106
1mf/l=1g/m3=1ppm
Precautions for ozone detection: The sampling tube material should be made of materials that are resistant to strong oxidation, such as glass, polytetrafluoroethylene, and polyvinylidene fluoride; Stainless steel materials should also be used as little as possible to reduce ozone loss in the sampling tube. The sampling tube should be as short as possible, and generally should not exceed 2 meters when measuring low concentrations. Do not leak air from the sampling tube to the detection instrument, otherwise the measurement value will be low. When detecting low concentrations of ozone (such as in the detection environment), the new PTFE tube should also undergo sufficient "ozone oxidation", which stabilizes the inner wall of the sampling tube by using gas containing high concentrations of ozone. Japanese company Ebara believes that it takes more than 20 minutes to stabilize, while American company Monet requires several hours. The sampling tube should be cleaned and dried regularly. Unclean sampling tubes can cause low measurement values. Ozone analyzers need to be calibrated regularly to ensure reliable measurement data.

Chemical detection method: iodometric method
The iodometric method is the most commonly used ozone determination method, and it is used as the standard method for measuring gas ozone in China and many other countries. The standard CJ/T3028.2-94 "Measurement of Ozone Concentration, Production, and Electricity Consumption of Ozone Generators" issued by the Ministry of Construction of China stipulates the use of the iodometric method. The principle is that strong oxidant ozone (O3) reacts with potassium iodide (KI) aqueous solution to generate free iodine (I2). Ozone is reduced to oxygen. The reaction equation is:
O3+2KI+H2O → O2+I2+2KOH
Free iodine color changes from light yellow to deep red depending on its concentration in water.
Titrate with sodium thiosulfate (NaS2O3) standard solution, free iodine is converted to (NaI), and the endpoint of the reaction is fading. The reaction equation is:
I2+2Na2S2O3 →2 NaI+NaS4O6
The quantitative relationship between O3 reaction amount and NaS2O3 consumption established by two reaction equations is 1mol O3:2mol NaS2O3. Therefore, the calculation formula for ozone concentration CO3 is:
CO3=40x3x1000/1000（mg/L）
Where:
CO3- ozone concentration, mg/L；
ANa - dosage of sodium thiosulfate standard solution, ml；
B - concentration of sodium thiosulfate standard solution, mol/L；
V0- Sampling volume of ozone gas, ml。
Refer to standard CJ/T3028.2-94 for operating procedures and methods.
It is convenient to determine the concentration of standard generators. The volume of ozone gas is counted using a flow meter, and the concentration of NaS2O3 is generally prepared at 0.100mol/L, with a measurement accuracy of ± 1%.
When measuring the concentration of ozone in the air, it should be used for quantitative extraction with an air sampler. To ensure measurement accuracy, NaS2O3 is prepared at a concentration of 0.10mol/L.
The concentration of water-soluble ozone can also be calculated using this formula, except that V0 represents the amount of water collected, taking 1000ml. The concentration of NaS2O3 is 0.10mol/L.
The advantage of iodometric method is its intuitive color development. No need for expensive instruments. The disadvantage is that it is susceptible to interference from oxidants such as NO and CI2, and the influence of other oxidants should be subtracted during important testing.

Colorimetry: Colorimetry is a method of determining ozone concentration based on the degree of color or decolorization reaction between ozone and different chemical reagents. According to colorimetric methods, it can be divided into artificial color sample colorimetry and photometer colorimetry This method is commonly used to detect the concentration of dissolved ozone in water
In China, colorimetric solutions such as potassium iodide and ortho dimethylamine are used to detect the dissolved ozone concentration in bottled water. The method is to use a colorimetric tube to compare the sample and determine the ozone solubility value (0.05-0.08mg/L) of the sample. If required, a spectrophotometer is used for detection.
It is very convenient for foreign countries to use this method to make instruments, prepare standard tools and drugs for on-site sampling. DPD (Dihexylphenylenediamine) colorimetric discs from HACH Corporation in the United States and Ebara Corporation in Japan, with a range of 0.05-2mg/L. HACH company's miniature colorimeter utilizes indigo dye decolorization reaction. At a wavelength of 600nm, the concentration is displayed as 0.05-0.75nm/L, with an accuracy of ± 0.01nm/L. Less interference from other oxidants. Detection tube: The ozone oxidation variable reagent is immersed in a carrier and packaged as a reactant in a standard inner diameter glass tube to make a detection tube. When in use, the two ends of the detection tube are cut off, and a vacuum pump is connected to the exhaust end of the detection tube to extract a quantitative amount of ozone gas. The ozone concentration is proportional to the length of the reagent column color change inside the detection tube, and the concentration value is read through the scale value.
Germany, Japan, and China all produce ozone detection tubes with concentration ranges of high (1000ppm), medium (10ppm), and low (3ppm). They are used to detect air ozone concentration and are suitable for on-site applications. They are easy to use, but have low accuracy (± 15%).