ISO/FDIS 7383-3

ISO/TC 281
Secretariat: JISC
Date: 2025-02-082026-04-10
Fine bubble technology — Evaluation method for determining gas
content in fine bubble dispersions in water —
Part 3:
Ozone content
FDIS stage
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ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle and application . 2
4.1 General. 2
4.2 Iodometric titration . 2
4.3 Ultraviolet photometry . 3
5 Apparatus and materials . 4
5.1 Iodometric titration . 4
5.2 Ultraviolet photometry . 4
6 Procedure . 6
6.1 Iodometric titration . 6
6.2 Ultraviolet photometry . 9
7 Results and calculation . 10
7.1 Iodometric titration . 10
7.2 Ultraviolet photometry . 10
8 Measurement errors . 10
8.1 Iodometric titration . 10
8.2 Ultraviolet photometry . 11
8.3 Standard deviation of the measurement . 11
9 Test report . 11
Annex A (informative) Influence of high DO levels on iodometric titration. 13
Annex B (informative) Example of a test result using iodometric titration in a testing laboratory15
Annex C (informative) Comparison of iodometric titration and UV photometry test results of
water samples with different UFB concentrations . 17
Annex D (informative) Example of continuous ozone-content measurements using UV
photometry . 20
Bibliography . 22

iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
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This document was prepared by Technical Committee ISO/TC 281, fineFine bubble technology.
A list of all parts in the ISO 7383 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
The integration of microbubble (MB) and ultrafine bubble (UFB) technologies with ozonation results in
considerably enhanced solubility and oxidative capacity of ozone. This innovative and effective approach has
been used for applications such as advanced treatment of recalcitrant wastewater, cleaning processes in the
semiconductor industry, and general cleaning tasks. Ozone concentration is a critical parameter in these
applications as it determines the effectiveness of the ozone MB and UFB generation equipment as well as the
efficiency of the cleaning processes. The ozone concentration needs to be accurately measured for evaluating
the performances of different ozone-generation systems and ensuring effectiveness of ozone-enriched water
products used in the abovementioned applications. Common methods for measuring ozone concentration in
water, such as electrochemical sensing via membrane-type polarography, iodometric titration, and ultraviolet
(UV) photometry, are unsuitable for water containing MBs and UFBs because bubbles introduce complexities
in reliable and precise measurements. To accurately determine ozone levels in such scenarios, the usual
methods require adaptations and specific considerations.
Membrane-type polarography has considerable limitations in determining ozone concentrations in water
containing microbubbles (MB) and ultrafine bubbles (UFBs). As the ozone in bubbles adhering to the electrode
surface can permeate the membrane and enter the electrolyte, the measured ozone concentration exceeds the
actual concentration in the water. Furthermore, deviation in measurement results increases with increasing
bubble number concentration because the affected surface area increases with increasing number of bubbles.
The flow rate of the fluid over the electrode surface is another critical factor; inappropriate flow rates mightdo
not always effectively remove the adhering bubbles, further impacting the measurement accuracy. Finally,
ozone at high concentrations can corrode the membrane used in the measurements, affecting its performance
and destabilizing the results. To ensure accuracy and reliability of ozone concentration determination,
membrane-type polarography requires specific adaptations such as a flow cell that maintains suitable flow
rates and regular checking and replacement of damaged membranes. This method can be used to measure the
ozone concentration in bubble-free water up to 20 mg/Ll but is unsuitable for concentrations exceeding this
threshold.
UV photometry also involves limitations in accurately determining the ozone concentration in water
containing MBs or UFBs; MBs and UFBs scatter and reflect UV light, thereby inflating the involved absorbance
measurements. Moreover, considerable scattering occurs for high bubble concentrations, so the quantity and
size of the bubbles further influence the measurements. Meanwhile, dynamic changes with regard to the
bubbles in water, such as formation and floating, can cause fluctuations in the absorbance readings,
complicating the measurement process. To mitigate such bubble effects, UV photometry in situations with
MBs and UFBs requires specific measures such as titration-based calibration and compensation using data
processing.
Although UFBs do not directly substantially impact the ozone concentration obtained using iodometric
titration in water containing MBs and UFBs, the dissolved-ozone concentration in the water can be altered
when the ozone molecules within the bubbles transition to a dissolved state. This change, which can manifest
as a “titration reflection” phenomenon, requires the operator to quickly and accurately adjust the speed and
amount of reagent addition to accommodate the changing concentration. Consequently, the single-
measurement titration time may be prolonged; the involved manual operations need to be performed at high
precision. Therefore, iodometric titration is appropriate for single measurements in a laboratory setting but
unsuitable for continuous online measurements.
This standarddocument recommends iodometric titration for single measurements of ozone concentration in
water containing MBs and UFBs. For online measurements, the data should be preliminarily corrected through
sodium thiosulfate titration and then analyzedanalysed via UV photometry in combination with a flow cell to
enhance the accuracy and reliability of continuous monitoring. The establishment of this standardthe method
in this document provides a common measurement approach for the ozone content, facilitating the
comparison and interpretation of the qualities and functions of ozone-based cleaning products.
v
ISO 20304-1 assesses the performance of ozone fine bubble systems through the decolourization of methylene
blue, which evaluates the oxidizing ability of the system without measuring the actual ozone concentration.
Although the methylene blue test effectively evaluates the treatment potential of ozone in certain applications,
it does not provide precise ozone concentration data, which are essential for applications demanding accurate
dosing and control.
Evaluation methods for determining oxygen and hydrogen contents in fine bubble dispersions in water have
been published as ISO 7383-1 and ISO 7383-2, respectively. Evaluation methods for determining reactive
oxygen species in UFB dispersions in water have also been published as ISO 24758-1 and ISO 24758-2. These
methods address reactive oxygen species and do not involve the determination of ozone content, which is the
focus of this document. An evaluation method for the ozone content is also necessary because ozone plays a
critical role in various advanced applications, particularly when integrated with MB and UFB technologies.
This document emphasizes the importance of accurately measuring the ozone content in water containing
MBs and UFBs and facilitates industrial applications requiring precise ozone dosing and control, thereby
supporting consistent quality assurance and performance evaluation in processes involving ozone MB and
UFB systems.
vi
Fine bubble technology — Evaluation method for determining gas
content in fine bubble dispersions in water —
Part 3:
Ozone content
1 Scope
This document specifies two evaluation methods for ozone content (total ozone, including ozone contained in
ultrafine bubbles (UFBs) or microbubbles (MBs) and dissolved ozone) in UFB dispersions in water, namely,
iodometric titration and UV photometry.
Iodometric titration is applicable as a well-established, high accuracy chemical procedure, particularly
suitable for single-point determinations. The direct measurement range of this technique is typically
0,01– mg/l to 50 mg/Ll.
Ultraviolet (UV) photometry is applicable for rapid or continuous measurement and real-time monitoring. Its
typical measurement range is from 0,075 mg/l to 200 mg/Ll, depending on instrument specification.
This document is applicable to industrial processes that require precise ozone dosing and control when MB
or UFB systems are used.
NOTE This document does not involve the specific effects of ozone UFB dispersion applications. High concentrations
of dissolved oxygen (DO), commonly found in water containing oxygen UFBs, can interfere with iodometric titration and
lead to overestimation of ozone content. When extremely high ozone levels are expected, water containing oxygen UFBs
maycan be used as the blank control.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 23015, Fine bubble technology — Measurement technique matrix for the characterization of fine bubbles
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
dissolved ozone
ozone molecules dissolved in water

3.2
ozone ultrafine bubble
ozone UFBsUFB
ultrafine bubbles bubble containing ozone molecules inside
3.3
titration
method that determines the concentration of a dissolved substance in terms of the smallest amount of a
reagent of known concentration that induces a given effect when reacted with a known volume of the test
solution
3.4
UV 254 nm
ultraviolet (UV) light with a wavelength of 254 nm, showing a peak in the UV absorption spectrum of ozone
Note 1 to entry: At this wavelength, UV light is compatible with the molecular structure and electronic configuration of
ozone and is efficiently absorbed
4 Principle and application
4.1 General
The following two methods given in 4.2 and 4.3 are available for ozone-content measurements in UFB
dispersions generated by cleaned UFB generation systems utilizing pure water, saline, or buffer solutions, and
in gaseous mixtures containing ozone. These two methods can complement each other to achieve accurate
and continuous determination of ozone content in water containing ozone UFBs.
Iodometric titration has a detection limit of 0,01 mg/Ll and is suitable for precise single-point determinations.
Prior to sample analysis, the pH of the sample shall be adjusted to 2,0 ± 0,1 using concentrated sulfuric acid of
approximately 3,1 mol/ L (6,2 N) to maintain the reactivity of ozone in the water. This method offers a wide
detection range with no upper limit. For more accurate measurements, water with a high concentration of
oxygen (higher than 20 mg/Ll) should be titrated to provide a background value.
UV photometry is appropriate for continuous sample analysis. Prior to measurement, the results read by the
instrument shall be calibrated using iodometric titration. The maximum detection limit of this method is
200 mg/Ll and the minimum limit (usually 0,075 mg/Ll) depends on the precision of the instrument.
Ozone in UFB dispersions is typically generated by passing pure oxygen through a high-voltage corona
discharge system. This process splits the oxygen molecules, which then recombine to form ozone. The
resulting ozone UFB dispersion primarily contains ozone and pure oxygen UFBs; nitrogen UFBs are present
in minimal amounts and can be ignored.
4.14.2 Iodometric titration
Iodometric titration relies on the reaction between ozone (strong oxidizing agent) and potassium iodide in
aqueous solution, which generates free iodine and reduces ozone to oxygen. The free iodine reacts with a
starch indicator, causing a colour change. During titration with a standard solution of sodium thiosulfate, the
free iodine transforms into sodium iodide. The endpointend point of the reaction is reached when the solution
completely decolourizes. The reaction equations are as follows:
O3 + 2KI + H2O → I2 (blue colour) + 2KOH+O2,
I + 2Na S O → 2NaI (colourless) + Na S O .
2 2 2 3 2 4 6
The stoichiometric ratio of ozone to sodium tetrathionate is 1:2.
Before titration, the pH of the sample to be tested shall be adjusted to 2,0 ± 0,1 using concentrated sulfuric
acid of approximately 3,1 mol/ Ll (6,2 N) to prevent the transformation of ozone into reactive oxygen species
such as hydroxyl radicals. This ensures that the titration process measures the ozone content itself rather than
the content of other reactive oxygen species in water. To correct for the effect of dissolved oxygen (DO)
throughout the titration process, a titration on water with a high oxygen concentration is performed as a
background.
This method allows the simultaneous determination of combined dissolved ozone and UFB-containing ozone
molecules in water.
4.24.3 Ultraviolet photometry
4.2.14.3.1 Principle of measuring ozone in water by ultraviolet photometry
Ozone strongly absorbs in the near UV, peaking at 254 nm. Interference from substances such as air, oxygen,
and water areis minimal in this spectral region.
The measurement of ozone in water is based on the attenuation of light as the sample passes through an
absorption cell with a quartz window. A low-pressure mercury lamp is positioned at one side of the cell, while
a photodiode equipped with an interference filter centeredcentred at 254 nm is placed at the other side.
Applying the Beer–Lambert law, the ozone concentration is calculated from the light-intensity difference
between ozone-containing and ozone-free water samples at the photodiode.
However, as this method is sensitive to bubbles and other impurities in the water, especially in water
containing ozone MBs or UFBs, the measurement results must be appropriately corrected.
Ultraviolet photometry at 254 nm maycan be subject to interference from natural organic matter and other
UV-absorbing substances present in real water samples. Therefore, this method is primarily applicable to
relatively clean water matrices, and its use in complex natural waters maycan require additional corrections
or validation.
4.2.24.3.2 Principle of correcting the results using iodometric titration
Instruments for UV photometry shall first be calibrated using iodometric titration to ensure accurate
measurements.
MBs and UFBs in water can lower the ozone concentration measured by UV photometry. To correct for the
influence of these bubbles, 5– to 10 ozone water samples containing UFBs are prepared and measured using
both iodometric titration and a commercially available UV photometry device that has been calibrated in
advance. The ozone concentrations determined by UV photometry and iodometric titration are plotted on the
x and y axes of a graph, respectively, and the results are linearly fitted. The fitted curve is represented by y = kx
+ b, where b (y-intercept) indicates the contribution of MBs or UFBs to the ozone concentration.
After establishing the standard curve, continuous readings of the ozone UFB dispersions are taken. The real
total ozone content in the ozone UFB dispersion is then obtained by multiplying the read values by k and
adding b to the result.
The presence of UFBs should be verified. Verification may be performed using a particle tracking analysis
method in accordance with ISO 19430, or by other methods described in ISO/TR 23015:2020.
5 Apparatus and materials
5.1 Iodometric titration
5.1.1 Reagents
5.1.1.1 1) Preparation of a 20 % potassium iodide solution: Dissolve 20 g of analytical-grade potassium
iodide in 80 mLml of distilled water that has been boiled and then cooled at 20 °C. Subsequently, make up the
volume to 100 mLml using volumetric flask and store the resultant in a brown bottle in the refrigerator. Stand
the solution for ≥ ≥ 1 d before use.
5.1.1.2 2) Preparation of a 1:5-diluted sulfuric acid solution: Measure 100 mLml of concentrated sulfuric
acid (18,4 M), and gradually add it while stirring into a beaker containing 500 mLml of distilled water.
5.1.1.3 3) Preparation of a 0,01-mol/Ll standard sodium thiosulfate solution: Weigh 0,248 g of analytical-
grade sodium thiosulfate pentahydrate, dissolve it in freshly boiled and cooled distilled water, and make up
the volume to 100 mLml in a volumetric flask.
5.1.1.4 4) Preparation of a 1 % starch indicator: Weigh 1 g of soluble starch, initially mix it with cold water
to form a suspension, then slowly add approximately 80 mLml of boiling water while stirring, and boil for
several minutes. After cooling, transfer the suspension to a 100-mLml volumetric flask and make up the
volume to 100 mLml using a volumetric flask. Allow the solids to settle overnight and use the supernatant
liquid for tests.
5.1.2 Apparatus
The following apparatuses are required: an iodineapparatus shall be used.
5.1.2.1 Iodine flask (or a stoppered conical flask), a measuring).
5.1.2.2 Measuring cylinder, a burette, a volumetric.
5.1.2.3 Burette.
5.1.2.4 Volumetric flask, and a retort.
5.1.2.15.1.2.5 Retort stand.
5.2 Ultraviolet photometry
5.2.1 Apparatus
The method employs a commercially available instrument equipped with a UV detector, flow cell, and water
pump. The UV detector contains a mercury lamp. The sample chamber is irradiated with 254-nm light passed
through a monochromatic filter. The signal from the chamber is captured by the detector, which calculates the
sample absorbance according to the Lambert–Beer law. This absorbance value is then converted into the
ozone concentration, which is directly displayed on the instrument’s dashboard. For accurate measurements,
a sample flow rate of 200 mLml/min is recommended.
When converting the absorbance to ozone concentration, the measured values can be corrected by adjusting
the instrument’s parameters based on the titration results, ensuring accurate measurements.
CAUTION — All piping in the UV measurement system shall be made of perfluoroalkoxy (PFA) or a
material with equivalent or superior resistance to ozone oxidation to prevent the release of chemicals
that couldcan interfere with the measurement accuracy. Additionally, the piping length shall be kept
as short as possible to minimize ozone loss during flow.
The measurement configuration is shown in Figure 1.
a) Overall view
b) Detailed structure of the UV detector
Key
1 ozone generator
2 UFB generator
3 reaction tank
4 UV detector
5 water pump
6 mercury lamp
7 monochromatic filter 254nm
8 ozone FB dispersion inlet
9 monochromatic UV beam
10 sample chamber
11 ozone FB dispersion outlet
12 detector
13 digital panel meter
Figure 1— Schematic of ultraviolet (UV) photometry for ozone measurements : (A) Overall view and
(B) detailed structure of the UV detector
5.2.2 Device for measuring UFB size and concentration
A device capable of measuring the size and concentration of UFBs in an ozone UFB dispersion shall be used. It
shall operate within a suitable particle-size measurement range (for example,e.g. 50– nm to 1 ,000 nm) and
provide adequate accuracy and repeatability. A particle tracking analysis method (see ISO 19430) may be used
as one example, and other methods described in ISO/TR 23015:2020 are also acceptable. Alternative
instruments with equivalent or superior characteristics may be employed. During the measurement, the water
temperature shall be maintained within 20 °C –to 25 °C and kept stable to within ±1 °C; the actual temperature
shall be recorded.
6 Procedure
6.1 Iodometric titration
6.1.1 General
The total procedure comprises three steps: pH adjustment (see 6.1.2,), titration detection (see 6.1.3,) and data
calculation (see 6.1.4.).
6.1.16.1.2 pH adjustment
Prior to ozone measurements, the pH value of the involved sample to be tested shall be adjusted to
2,0 ± 0,1 using strong acid. This step is crucial to prevent the transformation of ozone into other reactive
oxygen species such as hydroxyl radicals, ensuring that titration measures the ozone content itself rather than
the content of other reactive oxygen species in wate
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