Ozone concentration detection method
Ozone is a strong oxidizing agent with strong sterilizing, bleaching, and deodorizing properties. Therefore, it is widely used in products for water disinfection,
food processing sterilization and purification, food storage and preservation, medical care, and household disinfection and purification. In the production and
application of ozone generators, a certain ozone concentration is an important parameter to ensure the disinfection and oxidation effect, save energy and
prevent pollution.
1. Calibration of ozone generator output
The ozone production of the generator is its most important and basic technical indicator, and the production is calculated by measuring the ozone
concentration. Strictly speaking, without reliable means of measuring ozone concentration, it is impossible to produce qualified products. The current
false reports of ozone generator output on the market are mainly due to the lack of ozone concentration indicators or being untrue.
2. Ozone concentration ensures disinfection effect
Only by ensuring that, like other disinfectants, can the disinfection effect be achieved only by reaching a sufficient dose and acting for a certain period
of time. For example, when the ozone concentration is 0.08~0.6ppm, it will act on E. coli in bacterial propagules in the air for 30 minutes, and the average
killing rate will reach 84.60~99.9%. When the ozone concentration in the air is 0.34~0.85ppm, the effect will be 10~ In 30 minutes, the killing rate can reach
99.47~99.97%. Another example is when ozone disinfects the air. When the concentration is 0.21 mg/L, the killing rate of Staphylococcus aureus reaches
90.81% after 10 minutes of action. If the concentration is increased to 0.72 mg/L, the action time is still 10 minutes, and the killing rate is 90.81%. Up to
99.99%.Generally speaking, the higher the concentration of ozone, the better the bactericidal effect.
3. The ambient ozone concentration cannot be too high
In addition to being beneficial to humans, ozone is also a substance that pollutes the environment. my country's ambient air quality standards
(GB3095-1996) stipulate that the concentration limit of ozone (1 hour average) is 0.12mg/ m 3 ; the secondary standard is 0.16mg/m 3 ; the
third-level standard is 0.20mg/m 3 . The industrial hygiene standard for ozone in most countries has a maximum limit of 0.1ppm (0.20mg/m 3 ).
Therefore, the concentration of ozone disinfection and sterilization should not be too high, and the output of the ozone generator is not as high
as possible. For example: the output of an ozone generator for general household indoor sterilization should be around 200mg/h, and the
maximum should not exceed 400mg/h. In this way, after ozone sterilization works for 30 to 60 minutes, the indoor residual concentration is
lower than the health standards required by fruit producers. It should be noted that some people with allergies may experience symptoms
such as itchy skin, difficulty breathing, coughing and rhinitis after being exposed to an environment with ozone content exceeding 0.18 mg/m 3 f
or a long time. No matter how high the concentration is, it will cause greater harm to the human body.
4. Ozone application engineering and equipment need to monitor ozone concentration
The ozone generator's ability to generate ozone is largely affected by the humidity of the air source, cooling water temperature, aging
of the discharge surface, etc., so the ozone concentration must be tested frequently. For large-scale ozone equipment, it is best to install a
high-concentration ozone (gas) detector in the process, a dissolved ozone detector to detect the mixed water, and a detector to detect the
ozone concentration contained in the exhaust gas. In order to control the entire system in the best working condition.
Ozone concentration detection methods can be roughly divided into three categories: "chemical analysis methods", "physical analysis methods"
and "physical and chemical analysis methods".
1. Chemical detection method
1.1 Iodometric method
The iodometric method is the most commonly used ozone measurement method. my country and many countries use this method as a standard
method for measuring gas ozone. The "Measurement of Ozone Concentration, Output, and Power Consumption of Ozone Generators" standard CJ/T
issued by the Ministry of Construction of my country 3028.2-94 stipulates the use of iodometric method. The principle is that the strong oxidant ozone
(O 3 ) reacts with potassium iodide (KI) aqueous solution to generate free iodine (I 2 ). Ozone is reduced to oxygen. The reaction formula is:
O 3 + 2KI + H 2 O → O 2 + I 2 + 2KOH
Free iodine develops color from light yellow to deep red depending on the concentration in water from low to high.
Using sodium thiosulfate (NaS 2 O 3 ) standard solution for titration, free iodine changes into sodium iodide (NaI), and the reaction end point is
complete discoloration. The reaction formula is:
I 2 + 2Na 2 S 2 O 3 → 2NaI + NaS 4 O 6
The two reaction equations establish the quantitative relationship between the O 3 reaction amount and the NaS 2 O 3 consumption as 1molO 3
: 2mol NaS 2 O 3 , then the ozone concentration C O3 calculation formula is:
C O3 =40x3x1000/1000 (mg/L)
In the formula:
C O3 ——Ozone concentration, mg/L;
A Na - dosage of sodium thiosulfate standard solution, ml;
B ——Concentration of sodium thiosulfate standard solution, mol/L;
V 0 ——Ozonated gas sampling volume, ml.
The operating procedures and methods refer to standard CJ/T3028.2-94.
Determining the concentration of a standard generator is easy. The ozonated gas volume is counted with a flow meter. The NaS 2 O 3 concentration is
generally prepared at 0.100 mol/L, and the measurement accuracy can reach ± 1%.
When measuring the ozone concentration in the air, an air sampler should be used to extract and quantify the air. In order to ensure the measurement
accuracy, the NaS 2 O 3 dosage is 0.10mol/L.
This formula can also be used to measure the concentration of water-soluble ozone, except that V 0 represents the amount of water taken, which is 1000ml.
The concentration of NaS 2 O 3 is 0.10mol/L.
The advantage of the iodometric method is that the color development is intuitive. No expensive equipment is required. The disadvantage is that it is susceptible
to interference from its oxidants such as NO, CI 2 and other substances. The influence of other oxidizing substances should be eliminated during important detection.
1.2 Colorimetry
The colorimetric method is a method to determine the ozone concentration based on the degree of color development or decolorization reaction between ozone
and different chemical reagents. According to the colorimetric method, it is divided into artificial color sample colorimetry and photometric colorimetry. This method
is mostly 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 concentration of ozone in bottled water. The
method is to compare the chromogenic liquid tube of the test sample to determine the ozone solubility value of the test sample (0.05~0.08mg/L). If accuracy is required,
use a spectrophotometer to detect it.
This method is used abroad to make instruments and prepare standard tools and medicines for on-site sampling, which is very convenient. For example, the DPD
(dihexyl-p-phenylenediamine) color disc of the American HACH Company and the Japanese Ebara Company has a range of 0.05~2mg/L. The American HACH company's
micro colorimeter uses the decolorization reaction of indigo dye. Colorimetric at 600nm wavelength, 0.05~0.75nm/L concentration digital display, accuracy ± 0.01nm/L.
Less interference from other oxidants.
1.3 Detection tube
The ozone oxidation changeable reagent is impregnated on the carrier and used as a reactant to encapsulate it in a glass tube with a standard inner diameter to make
a test tube. When using, cut off both ends of the test tube and connect the air extractor to the outlet end of the test tube to absorb quantitative ozone gas. The ozone
concentration is proportional to the discoloration length of the reagent column in the detection tube, and the concentration value is read through the scale value.
Germany, Japan and my country all produce ozone detection tubes. The concentration ranges are divided into high (1000ppm), medium (10ppm) and low (3ppm).
They are used to detect air ozone concentration. They are suitable for on-site applications and are easy to use, but have low accuracy. (±15%).
2. Physical methods
The most popular physical method for ozone analysis in the world now is the ultraviolet absorption method. It is an analytical instrument that utilizes ozone's
characteristic absorption characteristics of ultraviolet light of 254nm wavelength and is manufactured based on the Beer-Lambert law. As long as an absorption
cell of appropriate length is selected, it can detect 0.002mg/m3~5% ( vol) concentration of ozone. The linear shape is good within 4 to 5 orders of magnitude.
This method has been adopted as the standard method for measuring ozone in ambient air in my country (GB1/T1154348).
