ISO 21910-1:2020

INTERNATIONAL ISO
STANDARD 21910-1
First edition
2020-01
Fine bubble technology —
Characterization of microbubbles —
Part 1:
Off-line evaluation of size index
Reference number
ISO 21910-1:2020(E)
©
ISO 2020

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ISO 21910-1:2020(E)

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© ISO 2020
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ISO 21910-1:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Requirements on the sample . 2
4.2 Requirements on the sample transfer and measurement system . 2
5 Measuring instruments . 3
6 Environment . 3
7 Sample transfer and measurement system . 3
7.1 General . 3
7.2 System structure . 3
7.3 Arrangement of components . 3
7.3.1 Position of the inlet tube mouth . 3
7.3.2 Position of the measuring instrument . 3
7.4 Retention container . 4
7.4.1 General. 4
7.4.2 Configuration requirements for retention container . 4
7.5 Loading tube . 5
7.5.1 Loading tube inner diameter. 5
7.5.2 Loading tube length . 5
7.5.3 Curvature of the loading tube . 5
7.5.4 Surface roughness . 5
7.5.5 Loading tube materials . . 5
7.5.6 Suppression of loading tube sway . 5
7.6 Loading pump . 5
7.6.1 General. 5
7.6.2 Flow rate (Flow velocity). 5
7.7 Retention time . 6
7.8 Dispersion before/during sampling for microbubbles with shell . 6
8 Procedure. 7
9 Data acquisition. 7
9.1 General . 7
9.2 Measurement time . 8
9.3 Number of measurements . 8
9.4 Size category . 8
9.5 Results . 8
9.6 Calibration and traceability . 8
9.7 Uncertainty evaluation . 8
10 Correction . 8
10.1 General . 8
10.2 Reserved water used for blank preparation . 8
11 Report . 9
Annex A (informative) Example of microbubbles without shell measurement using
dynamic image analysis .10
Annex B (informative) Effect of setting arrangement .14
Annex C (informative) Example of corrected data by subtraction of blank water .18
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ISO 21910-1:2020(E)

Annex D (informative) Example of method repeatability.19
Annex E (informative) Example of comparisons among 3 measurement techniques .20
Bibliography .22
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ISO 21910-1:2020(E)

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
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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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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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 21910 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.
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ISO 21910-1:2020(E)

Introduction
Recent development in the fine bubble technology expands its market, such as cleaning, water
treatment, agriculture and aquaculture as well as biomedical. Above all, the application of microbubble
technology accelerates the market penetration.
Many measurement technologies have been historically developed to assess the characteristics
of microbubbles and are now used in various application fields. However, the dynamic nature of
microbubbles makes it hard for the users to report their measurement results with confidence. The
low stability of microbubbles that includes shrinking, deformation, coalescence and dissolution of
individual microbubble can require a specific sampling procedure and short measurement time.
This document is intended to specify an evaluation method for size index of microbubbles in water to be
used in a measurement laboratory. The application of the document to measurement system will yield
comparable results over an application field, as far as the specified types of measuring instruments are
equipped and the specified sampling procedures are met. Since the comparability relevance depends on
the sampling procedures and the measurement environments, each measurement can require relevant
descriptions. The specifications of the measuring instruments are described in other standards or the
individual operation instruction manuals.
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INTERNATIONAL STANDARD ISO 21910-1:2020(E)
Fine bubble technology — Characterization of
microbubbles —
Part 1:
Off-line evaluation of size index
1 Scope
This document specifies the evaluation method for the size index of microbubbles in microbubble
dispersion. It is only applicable to microbubbles with or without shell in water within the range
from 1 μm to 100 μm. It describes the sampling methods from the point generating or dispersing
microbubbles in the retention container to the detecting point of the measuring instruments.
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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
measurement time
period for a sequence of measuring process, whereas the size index and/or the number concentration
index of the microbubbles can be assumed stable all through the period and reproducible over the
periods with similar measurement condition
Note 1 to entry: Measurement time is described by the starting time and the ending time, or by either of them and
the duration.
3.2
water diluent
homogeneous water which is used for dilution without causing any deleterious effects and whose
number concentration of ultrafine bubbles is known
Note 1 to entry: Water diluent is used to decrease the number concentration of ultrafine bubbles in a dispersion
without changing their total number, state of aggregation with particles, size or surface chemistry.
Note 2 to entry: Water diluent is called blank water when its number concentration of ultrafine bubbles is known
to be zero and when it is used for the evaluation of ultrafine bubbles.
[SOURCE: ISO 20298-1:2018, 3.2]
3.3
retention time
period from the point generating or dispersing microbubbles in the retention container to the detecting
point of the measuring instruments
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ISO 21910-1:2020(E)

3.4
method repeatability
closeness of agreement between multiple measurement results of a given property in different aliquots
of a sample, executed by the same operator in the same instrument under identical conditions within a
short period of time
Note 1 to entry: The variability includes those uncertainties due to operator sub sampling technique, any changes
in the sampled material together instrument variations.
[SOURCE: ISO 13320:2020, 3.22]
4 Requirements
4.1 Requirements on the sample
Microbubbles should be present in pure water or can be in tap water if the numbers of contaminant
particles are much lower than those of microbubbles. The microbubbles should contain air, nitrogen
and oxygen. In cases where they are surrounded with a coating, e.g. a lipid, other gas can be applied.
The size range of microbubbles that can be measured depends on the specification of the measuring
instrument to be used as is the number or volume concentration range of microbubbles. The reliability
of the results shall be confirmed for each measuring instrument.
Microbubbles which diameter is equal or larger than 10 μm should be measured promptly (see 7.6.1).
Microbubbles less than 10 μm and microbubbles with shell may not need to be measured quickly. This
classification is referred to in ISO 20480-2.
4.2 Requirements on the sample transfer and measurement system
An appropriate sample transfer and measurement system which connects a microbubble generating
system and a measuring instrument enable to characterize unstable microbubble dispersion in water
as a size index. Because of the low bubble stability of microbubbles without shell and the decrease in
dispersibility of microbubbles with shell, it is recommended to have the measuring instrument in the
vicinity of either the generating system or the dispersing system.
The size index of microbubbles should be determined just after the sample transfer. Signal acquisition
time of measuring instrument should be set at a minimum interval which is necessary for the detection
of sufficient signals from the microbubbles to determine its size index with good reproducibility. Before
loading the sample into a measuring instrument, clean the inside of a generating system by rinsing it
several times with water diluent to remove contaminants.
Attention should be paid to avoid microbubbles to adhere to the inside of the tube which is used for
loading to the measuring instrument.
Before each measurement, it should be confirmed if microbubbles are dispersed homogeneously or
saturated in water at a trial run.
Microbubbles with shell are inherently stable; however, they may settle down to the bottom of the
container. The procedure to measure microbubbles without shell can be applicable to measure
microbubbles with shell when they are dispersed uniformly during the measurement.
Storage or transportation of microbubbles without shell in microbubble dispersion is almost impossible
due to the low bubble stability.
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ISO 21910-1:2020(E)

5 Measuring instruments
Measuring instruments based on the following measurement techniques should be used to determine
the size index of microbubbles.
— Dynamic image analysis methods (see ISO 13322-2).
— Laser diffraction methods (see ISO 13320).
— Light extinction liquid-borne particle counter (see ISO 21501-3).
The reference of the method used shall be reported.
Refer to Annex E for an example of comparison among three measurement techniques.
6 Environment
The classification of air cleanliness should be applied for the measurement to prevent the contamination
of impurities.
Ambient temperature and atmospheric pressure should be stable to maintain the stability of
microbubble size.
7 Sample transfer and measurement system
7.1 General
The dynamic changes of microbubbles without shell may make it difficult to measure the microbubble
size. To obtain reproducible results with off-line measurement, the appropriate way to load microbubble
dispersion is the key technology to measure them promptly before they disappear.
For this purpose, the sample transfer and measurement system as shown in Figure 1 shall be used.
Essential information to define a sample transfer and measurement system is given in 7.2 to 7.7.
7.2 System structure
Microbubbles to be measured shall be generated or discharged in a retention container. The container
may work as a buffer to circulate microbubbles dispersion. The samples shall be sucked into a flow cell
using loading tube and loading pump set at the back of a flow cell.
7.3 Arrangement of components
7.3.1 Position of the inlet tube mouth
The position of the inlet tube mouth and the direction of it should be optimized for the spatial stability
at a trial run, or microbubbles should be measured at several positions to be averaged in consideration
to the velocity distribution in the retention container. If the position of the inlet tube mouth is set close
to the container wall and the surface of microbubbles dispersion, results may show low concentration.
If the position of the inlet tube mouth is set in front of outlet from
...