ISO 7383-3:2026

• Abstract:

  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/l. 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/l, 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 can be used as the blank control.

• Status: Published
• Publication Date: 13-Jul-2026
• ICS: 07.030 - Physics. Chemistry
• Technical Committee: ISO/TC 281 - Fine bubble technology
• Drafting Committee: ISO/TC 281/WG 2 - Fine bubble characterization and measurement
• Current Stage: 6060 - International Standard published
• Start Date: 14-Jul-2026
• Due Date: 20-Feb-2028
• Completion Date: 14-Jul-2026

Overview

ISO 7383-3: Fine bubble technology - Evaluation method for determining gas content in fine bubble dispersions in water - Part 3: Ozone content is an international standard developed by ISO/TC 281 to provide a reliable framework for accurately measuring ozone levels in water dispersions containing microbubbles (MBs) and ultrafine bubbles (UFBs). Accurate ozone content evaluation is critical for a range of industrial, environmental, and cleaning applications where ozone-enriched water is used. This standard specifies two robust evaluation methods:

• Iodometric titration for precise, single-point ozone measurement
• Ultraviolet (UV) photometry for rapid or continuous ozone monitoring

By offering standardized methods for determining ozone content, ISO 7383-3 facilitates quality assurance, process control, and product comparison in fine bubble technology applications.

Key Topics

• Scope and Importance

  • Addresses ozone measurement in water containing MBs and UFBs, including both dissolved and bubble-contained ozone
  • Crucial for industries requiring precision ozone dosing and monitoring for efficiency and safety

• Primary Evaluation Methods

  • Iodometric titration: A high-precision chemical assay suitable for single-point analysis with a typical detection range of 0.01 mg/L to 50 mg/L
  • UV photometry: Enables real-time and continuous ozone monitoring, with a range from 0.075 mg/L to 200 mg/L depending on instrument specifications

• Challenges Addressed

  • Traditional ozone measurement methods, such as membrane-type polarography, often yield inaccurate results in the presence of MBs or UFBs due to interference and bubble dynamics
  • UV photometry in MB/UFB dispersions requires specific calibration and correction strategies to mitigate absorbance distortions caused by bubble scattering

• Calibration & Correction

  • UV photometry must be calibrated against iodometric titration results for accuracy in bubble-laden samples
  • Measurement procedures include careful pH adjustment and consideration of dissolved oxygen interference

Applications

• Advanced Wastewater Treatment: Ensures effective ozonation for the removal of recalcitrant contaminants
• Semiconductor Manufacturing: Monitors cleaning processes where MB/UFB-ozone dispersions are vital for surface treatment
• Food Processing and Safety: Controls ozonated water dosing for sterilization, disinfection, and residue removal
• General Industrial Cleaning: Optimizes ozone levels in cleaning systems utilizing fine bubble technology for enhanced efficacy
• Environmental Monitoring: Supports research, monitoring, and regulatory compliance in natural and engineered water systems

Related Standards

ISO 7383-3 forms part of a broader suite of standards that bolster fine bubble technology measurement and application:

• ISO 7383-1: Evaluation method for determining oxygen content in fine bubble dispersions in water
• ISO 7383-2: Evaluation method for determining hydrogen content in fine bubble dispersions in water
• ISO 20304-1: Performance assessment for ozone fine bubble systems using methylene blue decolourization (does not directly measure ozone concentration)
• ISO 24758-1 & ISO 24758-2: Determining reactive oxygen species in UFB dispersions in water
• ISO 23015: Measurement techniques for characterization of fine bubbles
• ISO/TR 23015 & ISO 19430: Provide guidance on particle tracking analysis and other UFB measurement techniques

By referencing and integrating these ISO standards, organizations and laboratories can ensure comprehensive, accurate, and comparable data for quality and performance optimization in every application involving ozone-enriched fine bubble dispersions.

---

Keywords: ISO 7383-3, ozone content measurement, fine bubble technology, microbubbles, ultrafine bubbles, iodometric titration, UV photometry, ozone monitoring, water treatment, standard methods, ISO standards, gas content evaluation, ozone UFB dispersions.

International
Standard
ISO 7383-3
First edition
Fine bubble technology —
2026-07
Evaluation method for determining
gas content in fine bubble
dispersions in water —
Part 3:
Ozone content
Technologie des fines bulles — Méthode d'évaluation pour
déterminer la teneur en gaz dans les dispersions de fines bulles
dans l'eau —
Partie 3: Teneur en ozone
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
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
4.3.1 Principle of measuring ozone in water by ultraviolet photometry .3
4.3.2 Principle of correcting the results using iodometric titration .3
5 Apparatus and materials . 3
5.1 Iodometric titration .3
5.1.1 Reagents .3
5.1.2 Apparatus .4
5.2 Ultraviolet photometry .4
5.2.1 Apparatus .4
5.2.2 Device for measuring UFB size and concentration .5
6 Procedure . 6
6.1 Iodometric titration .6
6.1.1 General .6
6.1.2 pH adjustment.6
6.1.3 Titration detection .6
6.1.4 Data calculation . .7
6.1.5 Precautions .8
6.2 Ultraviolet photometry .8
6.2.1 General .8
6.2.2 Device calibration .8
6.2.3 Online testing .8
6.2.4 Accurate calculation of the real ozone content .8
7 Results and calculation . 9
7.1 Iodometric titration .9
7.1.1 Use of water containing oxygen UFBs as the blank control .9
7.1.2 Determination of ozone content in ozone UFB dispersions .9
7.2 Ultraviolet photometry .9
7.2.1 Determination of ozone content in solutions with UFBs .9
7.2.2 Online measurement and data verification .9
8 Measurement errors . 9
8.1 Iodometric titration .9
8.2 Ultraviolet photometry .10
8.3 Standard deviation of the measurement .10
9 Test report .10
Annex A (informative) Influence of high DO levels on iodometric titration .12
Annex B (informative) Example of a test result using iodometric titration in a testing laboratory . 14
Annex C (informative) Comparison of iodometric titration and UV photometry test results of
water samples with different UFB concentrations .16
Annex D (informative) Example of continuous ozone-content measurements using UV
photometry .18
Bibliography .20

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
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 ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 281, Fine 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 MBs 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 do 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/l 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 document 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 analysed via UV photometry in combination with a flow cell to
enhance the accuracy and reliability of continuous monitoring. The establishment of the 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.
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.

v
Evaluation methods for determining oxygen and hydrogen contents in fine bubble (FB) 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
International Standard ISO 7383-3:2026(en)
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/l.
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/l, 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 can be used as the blank control.
2 Normative references
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 UFB
ultrafine 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
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 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/l 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/l) 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/l and the minimum limit (usually 0,075 mg/l) 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.
4.2 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 end point of the reaction is reached when the solution
completely decolourizes. The reaction equations are as follows:
O + 2KI + H O → I (blue colour) + 2KOH+O
3 2 2 2
I + 2Na S O → 2NaI (colourless) + Na S O
2 2 2 3 2 4 6
The stoichiometric ratio of ozone to sodium thiosulfate 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/l (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.
4.3 Ultraviolet photometry
4.3.1 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 is 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 centred 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 can 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 can require additional corrections or
validation.
4.3.2 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 Preparation of a 20 % potassium iodide solution: Dissolve 20 g of analytical-grade potassium
iodide in 80 ml of distilled water that has been boiled and then cooled at 20 °C. Subsequently, make up the
volume to 100 ml using a volumetric flask and store the resultant in a brown bottle in the refrigerator. Allow
the solution to stand for ≥ 1 day before use.
5.1.1.2 Preparation of a 1:5-diluted sulfuric acid solution: Measure 100 ml of concentrated sulfuric acid
(18,4 M), and gradually add it while stirring into a beaker containing 500 ml of distilled water.

--
...