ISO 7383-2:2024

Fine bubble technology — Evaluation method for determining gas content in fine bubble dispersions in water — Part 2: Hydrogen content

This document specifies the evaluation methods for hydrogen content in ultrafine bubble (UFB) dispersions. The titration (oxidimetry) method can be used as a quick method to estimate the hydrogen content in hydrogen UFB dispersions. The lower limit of detection is 0,1 mg/l, and the range with acceptable accuracy is between 0,2 mg/l and 1,6 mg/l. The existence of oxidizing or reducing substances in dispersions influences measurement accuracy. The gas chromatographic method features a considerably high accuracy range and lower limit of detection. The existence of UFBs in water does not influence the measurement results. The existence of oxidizing or reducing substances in water does not affect the measurement accuracy either. However, the measurement procedure is time consuming. NOTE This document only provides a method for determining hydrogen contents in UFB dispersions and does not involve the specific effects of hydrogen UFB dispersion application.

Technologie des fines bulles — Méthode d'évaluation pour déterminer la teneur en gaz dans les dispersions de fines bulles dans l'eau — Partie 2: Teneur en hydrogène

General Information

• Status: Published
• Publication Date: 30-Jun-2024
• ICS: 07.030 - Physics. Chemistry
• Technical Committee: ISO/TC 281 - Fine bubble technology
• Drafting Committee: ISO/TC 281 - Fine bubble technology
• Current Stage: 6060 - International Standard published
• Start Date: 01-Jul-2024
• Due Date: 28-Aug-2026
• Completion Date: 01-Jul-2024

Standards Content (Sample)

International
Standard
ISO 7383-2
First edition
Fine bubble technology —
2024-07
Evaluation method for determining
gas content in fine bubble
dispersions in water —
Part 2:
Hydrogen content
Reference number
© ISO 2024
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 .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle and application . . 2
4.1 General .2
4.2 Titration (oxidimetry) method .2
4.3 Gas chromatography .2
5 Apparatus and materials . 2
5.1 Titration (oxidimetry) method .2
5.1.1 Reagent .2
5.1.2 Dropper or titrator .3
5.1.3 Clear vial .3
5.2 Gas chromatography .3
5.2.1 Vial and clamping machine .3
5.2.2 UFBs elimination .3
5.2.3 Carrier gases and column .3
5.2.4 Gas chromatograph .3
5.2.5 Measurement device for UFB size and concentration .4
6 Procedure . 4
6.1 Titration (oxidimetry) method .4
6.2 Gas chromatography .4
6.2.1 General .4
6.2.2 Sample sealing .5
6.2.3 UFBs elimination .6
6.2.4 Analysis of gas substitutes .6
7 Results and calculation . 8
7.1 Titration (oxidimetry) method .8
7.2 Gas chromatography .8
7.2.1 General .8
7.2.2 Calibration curve for hydrogen concentration measurement .8
7.2.3 Volume of the water sample in the vial .9
7.2.4 Volume of the headspace above the UFB dispersion in the vial .9
7.2.5 Pressure of the gas in the vial headspace .10
7.2.6 Hydrogen content in the vial head space .10
7.2.7 Hydrogen content in the vial water sample .10
7.2.8 Hydrogen content in association with each number concentration of UFBs and
dissolved hydrogen .11
8 Error of measurement .12
8.1 Titration (oxidimetry) method . 12
8.2 Gas chromatography . 12
8.3 Relative standard deviation of the gas chromatograph . 13
9 Test report .13
9.1 Testing results. 13
9.2 Testing conditions . 13
Annex A (informative) Example of test result at testing laboratory by titration (oxidimetry)
method . 14
Annex B (informative) Example of test result at testing laboratory by gas chromatography
using the capillary column . . 17

iii
Annex C (informative) Example of test result at testing laboratory by gas chromatography
using the packed column.20
Annex D (informative) Comparison of different vials when testing the hydrogen content by gas
chromatography .23
Bibliography .25

iv
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.

v
Introduction
Hydrogen has recently attracted considerable research attention across several fields, such as agriculture,
food, environment, and medicine sciences, owing to its antioxidant capacity and zero-residual and ecofriendly
properties. Hydrogen concentration is a crucial parameter to ensure its successful hydrogen application.
At present, there are potential limitations regarding the application of hydrogen in living organisms,
such as accessibility, availability, and biological intake. For example, hydrogen exhibits low solubility,
with a saturation concentration of only 1,6 mg/l. Fine bubble and ultrafine bubble (UFB) technology have
been used to address the low solubility of hydrogen in recent years. UFBs have a large surface area, high
internal pressure, and negatively charged surfaces, which accelerate the dissolution of gas into liquids and
maintain their stability in the liquids for relatively long periods. Therefore, UFBs can potentially expand the
application of hydrogen molecules because of their unique characteristics.
An accurate hydrogen concentration measurement is required to develop an impact evaluation standard for
the variety of hydrogen production equipment and hydrogen-rich water products. Normal techniques for
measuring the hydrogen content in water include the electrochemical probe (membrane-type polarography)
method, titration (oxidimetry) method using a methylene blue (MB)–platinum colloid reagent, and gas
chromatography.
The electrochemical probe (membrane-type polarography) method is advantageous as it can be used
for both in situ and real-time measurements. Detection limits are stated in the instruction manuals of
instruments and, in most cases, are approximately 0,01 mg/l. The upper limit depends on the specifications
of the instrument, but it is generally lower than 20 mg/l. Electrochemical probe methods can measure only
the dissolved hydrogen concentration in hydrogen UFB dispersions under a steady state or flow state and are
not suitable for static water samples. Additionally, the presence of UFBs in water can influence measurement
results.
The titration (oxidimetry) method is straightforward and economical; however, its lower limit of detection is
only 0,1 mg/l, and the titration range with acceptable accuracy is narrow. Moreover, hydrogen evaporation
during measurements and the presence of UFBs in water can influence measurements. Thus, this method
can be used only to approximate hydrogen concentrations in UFB dispersions.
Gas chromatography is the most accurate method for measuring the hydrogen content of gas. Its lower limit
of detection is the lowest among all methods, and there are no upper measurement limits. However, few
attempts have been made to apply this method to measuring hydrogen contents in water. Furthermore,
appropriate sample preparation and UFB elimination methods have yet to be developed.
Therefore, a standard method for measuring total hydrogen contents in UFB dispersions has been established.
For this document, the titration (oxidimetry) method is proposed as a rapid estimation method and gas
chromatography is proposed as an accurate measurement method. The following procedure was used for gas
chromatography. First, a bubble-elimination pretreatment is performed to drive both dissolved hydrogen
and hydrogen in UFBs from the liquid phase into the headspace, followed by gas chromatography combined
with theoretical calculations to determine the total hydrogen content in UFB dispersions. The establishment
of this standard method will serve various hydrogen production enterprises, the corresponding customers,
and research institutions, enabling them to have a common measurement standard when determining
hydrogen contents, thereby facilitating comparisons and judgments of the quality and function of hydrogen
products.
The standardized evaluation method for hydrogen content provides an important theoretical basis for
future applications in several fields, with further potential for industry, commerce, government, consumers,
and academic and research bodies. The establishment of standards will enable governments to establish
policies, regulate the development of the hydrogen health industry, and promote research and development
into products and technologies related to hydrogen agriculture, hydrogen medicine, and hydrogen-based
environmental applications.
vi
International Standard ISO 7383-2:2024(en)
Fine bubble technology — Evaluation method for determining
gas content in fine bubble dispersions in water —
Part 2:
Hydrogen content
1 Scope
This document specifies the evaluation methods for hydrogen content in ultrafine bubble (UFB) dispersions.
The titration (oxidimetry) method can be used as a quick method to estimate the hydrogen content in
hydrogen UFB dispersions. The lower limit of detection is 0,1 mg/l, and the range with acceptable accuracy is
between 0,2 mg/l and 1,6 mg/l. The existence of oxidizing or reducing substances in dispersions influences
measurement accuracy.
The gas chromatographic method features a considerably high accuracy range and lower limit of detection.
The existence of UFBs in water does not influence the measurement results. The existence of oxidizing or
reducing substances in water does not affect the measurement accuracy either. However, the measurement
procedure is time consuming.
NOTE This document only provides a method for determining hydrogen contents in UFB dispersions and does not
involve the specific effects of hydrogen UFB dispersion application.
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 hydrogen
DH
hydrogen molecules, dissolved in a liquid
3.2
hydrogen UFB
hydrogen molecules, dissolved as ultrafine bubble (UFB)
3.3
titration
method or process of determining the concentration of a dissolved substance in terms of the smallest
amount of a reagent of known concentration required to bring about a given effect in reaction with a known
volume of the test solution
4 Principle and application
4.1 General
The following two methods can be employed for hydrogen content measurements in UFB dispersions, which
are generated by cleaned UFB generation systems utilizing pure water, saline, or buffer solutions, and the
gas in which can be pure hydrogen or a gaseous mixture containing hydrogen.
The titration (oxidimetry) method is a quick, economical method with a lower limit of detection of 0,1 mg/l;
it is recommended for use only as a rough estimation method.
NOTE The existence of oxidizing or reducing substances in the dispersions influences measurement accuracy.
Gas chromatography is a method with higher accuracy, but it is more expensive and time consuming; it is
recommended to be used for more accurate hydrogen content measurements in UFB dispersions and as the
reference for the validation titration method.
4.2 Titration (oxidimetry) method
The titration (oxidimetry) method involves a redox reaction of a MB oxidant in the presence of a colloidal
platinum catalyst. MB generally reacts with an equimolar amount of hydrogen with platinum or palladium
to produce colorless, reduced MB (leucomethylene blue, leucoMB), as shown below:
+ −
MB (blue) + 2H + 2e →leucoMB (colorless).
The oxidimetry determination of the hydrogen concentration was performed by redox titration. The MB–
platinum reagent was added dropwise to a 6 ml sample of a hydrogen UFB dispersion until the solution
changed from blue to colourless.
If 6 ml of hydrogen dispersion reduces one drop (20 μl) of the MB–platinum reagent, the concentration of
dissolved hydrogen is 0,1 mg/l.
4.3 Gas chromatography
After the hydrogen UFB dispersion is sealed in a vial, the rubber stopper made of butyl rubber and aluminium
cap can effectively prevent the diffusion of hydrogen molecules. Through the change of the hydrogen UFB
dispersions from a liquid phase to a solid phase by the freezing process, the hydrogen molecules that
dissolve in the dispersions are transferred to the gas phase in the vial. Thereafter, the gas components in the
vial were separated into electrical signals that were sent to signal processing devices (computer) to obtain
peaks corresponding to the separated gas components. Resultantly, the molar concentration of the hydrogen
released from the UFB dispersions can be measured. Finally, the total hydrogen content in the hydrogen UFB
dispersion can be calculated.
5 Apparatus and materials
5.1 Titration (oxidimetry) method
5.1.1 Reagent
5.1.1.1 MB, C H CIN S Mass mol: 319,86 g/mol.
16 18 3
Form: brownish-red powder
Grade: analytical pure
5.1.1.2 Ethanol, C H O ⋅ 98 % (GC) Mass mol: 46,07 g/mol.
2 6
5.1.1.3 Colloidal platinum, Pt concentration 2 g/kg.
5.1.2 Dropper or titrator
Plastic Pasteur pipette (dropper) commonly comes in 1 ml, 2 ml, 3 ml, and 5 ml which comes with a specific
drop size of 10 µl, 20 µl, 25 µl, 35 µl, and 50 µl. For 2 ml plastic Pasteur pipette, one drop of the dropper
should be approximately 17 mg or 0,02 ml in the MB–platinum reagent.
To reduce the dosing error, a pipettor covering a volume range of 0 μl to 20 μl can be used instead of a
dropper; a commercial titrator can be used as well.
5.1.3 Clear vial
The vial had 6 ml graduated marks, and the colour change of the solution in the vial can be seen clearly.
5.2 Gas chromatography
5.2.1 Vial and clamping machine
5.2.1.1 Vial, made of borosilicate glass; the recommended volume of the vial was 100 ml. However, if the
amount of water is less, volumes as low as 15 ml are also acceptable. In Annex D, the comparative results of
the same water sample measured in different vials are displayed.
5.2.1.2 Rubber stopper, made of butyl rubber.
5.2.1.3 Cap, made of aluminium.
5.2.1.4 Clamping machine for a flip-top-cap.
5.2.2 UFBs elimination
5.2.2.1 4 °C-refrigerator.
5.2.2.2 −20 °C-freezer.
5.2.3 Carrier gases and column
5.2.3.1 Carrier gas, argon (Ar) or helium (He).
5.2.3.2 Standard hydrogen, can be obtained from a gas company or hydrogen generator (purity >
99,99 %).
5.2.3.3 Hydrogen calibration gases with 0,5 %, 1 %, 5 %, 10 %, 20 %, 50 % and 100 % hydrogen
concentrations in air.
5.2.3.4 Gastight plunger syringe, 1 ml in volume.
5.2.3.5 Chromatographic column, molecular sieve 5A capillary/plot columns (Msieve-5A or MolSieve-5A).
5.2.4 Gas chromatograph
A thermal conductivity detector (TCD) should be equipped for gas chromatography for the detection of
hydrogen gas present in an air mixture.

5.2.5 Measurement device for UFB size and concentration
The size and concentration of the hydrogen UFB dispersion are measured using a nanoparticle tracking analysis
1)
(NTA) instrument (see ISO 19430). The instrument used was a ZetaView® , allowing a measuring range from
50 nm to 1 000 nm. The wavelength of the laser light source was 488 nm. Alternative instruments with similar
or superior characteristics can also be used. The measuring temperature was approximately 15 °C.
6 Procedure
6.1 Titration (oxidimetry) method
MB (0,3 g) was dissolved in 98 % ethanol (98,9 g) to obtain a solution of MB in ethanol. An aqueous suspension
of 2 % colloidal platinum (0,8 g) was added to the solution, and the mixture was stirred to produce 100 g of
the MB–platinum reagent.
The MB–platinum reagent was added dropwise to a 6 ml sample of hydrogen UFB dispersions until the
solution changed from blue to colourless (see Figure 1). Thereafter, the MB–platinum reagent was added
using a dropper. To prevent uneven dropper volume, a pipettor covering a volume range of 0 μl to 20 μl was
used to add the MB–platinum reagent to the water sample (20 μl each time).
Key
A MB–platinum reagent added dropwise to sample
B solution changed from blue to colourless
C titration endpoint
Figure 1 — Image of the titration process
6.2 Gas chromatography
6.2.1 General
The total procedure consisted of three steps: sample sealing, UFBs elimination, and the analysis of gas
substitutes. The setup is shown in Figure 2. The detailed processes are as follows.
1) ZetaView® is an example of a suitable product available commercially. This information is given for the convenience
of users of this document and does not constitute an endorsement by ISO of this product.

Figure 2 — General view of gas chromatography system
6.2.2 Sample sealing
A freshly-prepared hydrogen UFB dispersion was placed in a sealed vial.
If the sample is a freshly-prepared dispersion with microbubbles and you wish to exclude the hydrogen
content within these microbubbles from your measurement, the sample shall be allowed to settle until the
water changes from its initial milky a
...