**2.2 Measurement methods**

It is necessary to determine the concentration of ozone produced by an ozone generator because of efficiency of processes, costs, excessive ozone, and environmental drawback [14, 16]. Many analytical methods for the determination of ozone concentration have been described in the literature. However, most of them are not specific and often give incorrect results [17]. Analysis of ozone is difficult because of the instability of pure ozone, volatilization from solution, the rapid decomposition of ozone in water, and the reaction with trace contaminants in water, etc. [18].

Ozone can be analyzed by methods given below [15]:


The last four methods are not commonly used for analysis. It is necessary to be aware of its reactivity, instability, volatility, and the potential effect of interfering substances to measure the amount of ozone in water correctly. Ozone sometimes is sprinkled in drops by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution in order to eliminate interferences [14].

### *2.2.1 Iodometric methods*

Gaseous ozone from ozone generator is absorbed by aqueous potassium iodide solution. On the other hand, a preformed ozone solution can be alternatively treated with aqueous potassium iodide solution. The liberated iodine is measured by spectrometer or titration with sodium thiosulfate. The pH value of iodine solution is adjusted to 2. Then, it is titrated with titrant solution sodium thiosulfate and starch indicator [14, 19–21]. Theoretically, one molecule of ozone releases one molecule of iodine as the triiodide ion. It is a standard method [21]. Oxidants like H2O2 and NOx are problem for the measurement method because of their interference with the analysis. The method is sensitive to pH, buffer composition, buffer concentration, iodide concentration, sampling techniques, temperature, and time [14, 19, 21].

Aqueous ozone solution is added to 2% potassium iodide in 0.1 M neutral phosphate buffer containing a known amount of arsenic (III). And then, the excess As (III) is back-titrated with standard iodine using a starch end point [21, 22].

Standard method for residual chlorine analysis is adapted for residual ozone as Palin DPD (N,N-diethyl-p-phenylenediamine) method. Ozone oxidizes iodine ion in phosphate buffer of pH 6.4. Then, the released iodine oxidizes DPD, and it is measured colorimetrically or is titrated with standard ferrous ammonium sulfate due to the formation of pink Wurster cation [21].

The other adapted standard way is amperometric method. Ozone oxidizes iodide ion in acetate buffer of pH 4.0–4.5 in the presence of sodium thiosulfate, phenylarsine oxide (PAO), or inorganic arsenic (III). These reagents are titrated with standard iodine to an amperometric end point without acidification. Grundwell et al. compared (**Table 1**) the four currently popular iodometric methods for aqueous ozone analysis in 2008 [21].

#### *2.2.2 Direct spectrometry*

Ozone has a peak absorption at 254 nm wavelength, and it is the ultraviolet spectrum, so absorbance of the gaseous ozone can be measured at 254 nm by direct UV spectrometry. The method is sensitive in the molar absorptivity. Interference of CO, hydrocarbons, NOx, or H2O vapor has no noticeable effects on measurement.

**17**

**Figure 3.**

*Use of Ozone in the Textile Industry*

Iodometric Amperometric As (III) back DPD

**Table 1.**

impurities [14, 19, 23–25].

[14].

*2.2.3 Colorimetric spectrometry*

*Iodometric methods for ozone analysis [21].*

stoichiometry of the reaction [17, 19].

*Ozonation of potassium indigo trisulfonate [26].*

*DOI: http://dx.doi.org/10.5772/intechopen.81774*

None

As (III) DPD

S2O3 = PAO or As (III)

UV absorbance measurement method is mainly useful for gas analysis. This method also can be used for measuring aqueous ozone solution. However, interference from turbidity, dissolved inorganics, and organics is a problem. Ozone is sprinkled into the gas phase in order to eliminate interference for measurement. If the sample is liquid, the best sample for this method will be clean water free of UV-absorbing

**Method O3 reduction I2 titration**

**Excess reagent pH pH**

3.5–9 4.5 6.8 6.4

2 4.2–6.8 6.8 6.4

Several different colorimetric methods are used for measuring ozone residuals. But most of them are sensitive to significant interference from secondary oxidants

The first reagents for measuring ozone in air and exhaust gases are indigo and its water-soluble derivatives, the sulfonated indigo compounds like indigo disulfonate, indigo carmine, and indigo trisulfonate. Water-soluble derivatives of indigo, indigo disulfonate, and indigo trisulfonate are pH or redox indicators. Purity and age of the indigo trisulfonate are very important for the method because they affect the

The indigo molecule contains only one double bond (C═C). It reacts with ozone in order to produce sulfonated isatin and similar substance (**Figure 3**). Maximum absorbance of indigo is at 600 nm [17, 26]. If the pH value is below 4, sensitivity of the method does not vary with ozone concentration, small changes of temperature of reaction, or the chemical composition of the water. The advantage of the method is applicable for lake water, too hard groundwaters, and biologically treated domestic wastewater. Indigo trisulfonate method is quantitative, selective, fast, and simple. Classical instrumentation of water work laboratories is enough for measurement. The method is based on the decolorization of the dye by ozone. The loss of color is directly proportional to the concentration of ozone, and pH value of the sample is adjusted to about 2 in order to minimize destruction of the ozone by hydroxide ions [17, 19, 21]. The concentration is the difference in absorbance between sample and blank [16]. Mn+2 ion is a problem in this method. Because, oxidation products from the reaction of Mn+2 ions with ozone can demolish indigo trisulfonate. So, glycine is added to the sample in order to demolish the ozone


### **Table 1.**

*Textile Industry and Environment*

• chemiluminescence,

• thermal conductivity,

*2.2.1 Iodometric methods*

• gas-phase titration with NO, and

• isothermal pressure change on decomposition.

due to the formation of pink Wurster cation [21].

ozone analysis in 2008 [21].

*2.2.2 Direct spectrometry*

tion in a clean solution in order to eliminate interferences [14].

The last four methods are not commonly used for analysis. It is necessary to be aware of its reactivity, instability, volatility, and the potential effect of interfering substances to measure the amount of ozone in water correctly. Ozone sometimes is sprinkled in drops by using an inert gas for analysis in the gas phase or on reabsorp-

Gaseous ozone from ozone generator is absorbed by aqueous potassium iodide

treated with aqueous potassium iodide solution. The liberated iodine is measured by spectrometer or titration with sodium thiosulfate. The pH value of iodine solution is adjusted to 2. Then, it is titrated with titrant solution sodium thiosulfate and starch indicator [14, 19–21]. Theoretically, one molecule of ozone releases one molecule of iodine as the triiodide ion. It is a standard method [21]. Oxidants like H2O2 and NOx are problem for the measurement method because of their interference with the analysis. The method is sensitive to pH, buffer composition, buffer concentration, iodide concentration, sampling techniques, temperature, and time [14, 19, 21]. Aqueous ozone solution is added to 2% potassium iodide in 0.1 M neutral phosphate buffer containing a known amount of arsenic (III). And then, the excess As (III) is back-titrated with standard iodine using a starch end point [21, 22]. Standard method for residual chlorine analysis is adapted for residual ozone as Palin DPD (N,N-diethyl-p-phenylenediamine) method. Ozone oxidizes iodine ion in phosphate buffer of pH 6.4. Then, the released iodine oxidizes DPD, and it is measured colorimetrically or is titrated with standard ferrous ammonium sulfate

The other adapted standard way is amperometric method. Ozone oxidizes iodide

ion in acetate buffer of pH 4.0–4.5 in the presence of sodium thiosulfate, phenylarsine oxide (PAO), or inorganic arsenic (III). These reagents are titrated with standard iodine to an amperometric end point without acidification. Grundwell et al. compared (**Table 1**) the four currently popular iodometric methods for aqueous

Ozone has a peak absorption at 254 nm wavelength, and it is the ultraviolet spectrum, so absorbance of the gaseous ozone can be measured at 254 nm by direct UV spectrometry. The method is sensitive in the molar absorptivity. Interference of CO, hydrocarbons, NOx, or H2O vapor has no noticeable effects on measurement.

solution. On the other hand, a preformed ozone solution can be alternatively

• oxidation-reduction potential (ORP),

• amperometry,

• calorimetry,

**16**

*Iodometric methods for ozone analysis [21].*

UV absorbance measurement method is mainly useful for gas analysis. This method also can be used for measuring aqueous ozone solution. However, interference from turbidity, dissolved inorganics, and organics is a problem. Ozone is sprinkled into the gas phase in order to eliminate interference for measurement. If the sample is liquid, the best sample for this method will be clean water free of UV-absorbing impurities [14, 19, 23–25].
