FprEN ISO 21362

SLOVENSKI STANDARD
oSIST prEN ISO 21362:2024
01-november-2024
Nanotehnologije - Analiza nanoobjektov s frakcioniranjem asimetričnega in
centrifugalnega pretoka skozi polje (ISO/DIS 21362:2024)
Nanotechnologies - Analysis of nano-objects using asymmetrical flow and centrifugal
field-flow fractionation (ISO/DIS 21362:2024)
Nanotechnologien - Analyse von Nanoobjekten mit Hilfe von Asymmetrischer-Fluss-
Feldflussfraktionierung und zentrifugaler Feldflussfraktionierung (ISO/DIS 21362:2024)
Nanotechnologies - Analyse des nano-objets par fractionnement flux asymétrique et flux
force centrifuge (ISO/DIS 21362:2024)
Ta slovenski standard je istoveten z: prEN ISO 21362
ICS:
07.120 Nanotehnologije Nanotechnologies
oSIST prEN ISO 21362:2024 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN ISO 21362:2024
oSIST prEN ISO 21362:2024
DRAFT
International
Standard
ISO/DIS 21362
ISO/TC 229
Nanotechnologies — Analysis of
Secretariat: BSI
nano-objects using asymmetrical
Voting begins on:
flow and centrifugal field-flow
2024-09-02
fractionation
Voting terminates on:
ICS: 07.120
2024-11-25
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Reference number
ISO/DIS 21362:2024(en)
oSIST prEN ISO 21362:2024
DRAFT
ISO/DIS 21362:2024(en)
International
Standard
ISO/DIS 21362
ISO/TC 229
Nanotechnologies — Analysis of
Secretariat: BSI
nano-objects using asymmetrical
Voting begins on:
flow and centrifugal field-flow
fractionation
Voting terminates on:
ICS: 07.120
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
Member bodies are requested to consult relevant national interests in IEC/TC AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
113 before casting their ballot to the e-Balloting application.
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
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Published in Switzerland Reference number
ISO/DIS 21362:2024(en)
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oSIST prEN ISO 21362:2024
ISO/DIS 21362:2024(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 7
5 Principles of operation . 9
5.1 Field-flow fractionation (General) .9
5.2 Specific applications by applied field.11
5.2.1 Flow field .11
5.2.2 Centrifugal field . 12
6 Method development for AF4. 14
6.1 General .14
6.2 Sample specifications . 15
6.3 Mobile phase specifications .16
6.4 Fractionation .16
6.4.1 Channel and membrane selection .16
6.4.2 Injection and relaxation .18
6.4.3 Optimizing flow conditions .19
6.4.4 Elution programme .19
6.4.5 Using FFF theory to select initial flow settings . 20
7 Method development for CF3 .21
7.1 General .21
7.2 Choice of mobile phase .21
7.3 Field strength selection .21
7.4 Field decay programme .21
7.5 Channel flow rate selection . 22
7.6 Calculation of the relaxation time . 22
7.7 Calculation of sample injection delay . 22
7.8 Using FFF theory to select initial settings . 22
8 Analysis of nano-objects .23
8.1 General . 23
8.2 Online size analysis . 23
8.3 Online concentration analysis .24
8.3.1 General .24
8.3.2 Mass-based methods . 25
8.3.3 Number-based methods . . 25
8.4 Online material identification or composition . 26
8.5 Off-line analysis (fraction collection) .27
8.6 Alternative and emerging methods .27
9 Qualification, performance criteria and measurement uncertainty .28
9.1 System qualification and quality control . 28
9.1.1 Basic system qualification . 28
9.1.2 Focusing performance . 29
9.1.3 Flow rate of the carrier liquid. 29
9.1.4 Separation field . 30
9.2 Method performance criteria . 30
9.2.1 Recovery . 30
9.2.2 Selectivity .31
9.2.3 Retention ratio .31
9.2.4 Resolution .31

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9.3 Method precision and measurement uncertainty .31
10 General procedures for measurement of samples .32
10.1 Introduction .32
10.2 Calibration of retention time for online size analysis .32
10.2.1 Calibration of the AF4 channel.32
10.2.2 Calibration of AF4 retention time for online size measurements . 33
10.3 AF4 general measurement procedure . 33
10.4 CF3 general measurement procedure. 34
11 Test report .35
11.1 General . 35
11.2 Apparatus and measurement parameters . 35
11.2.1 AF4 recording/reporting specifications . 35
11.2.2 CF3 recording/reporting specifications . 36
11.3 Reporting test results . 36
Annex A (informative) Summary of interlaboratory comparison .38
Bibliography .52

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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 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 any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following URL:
www.iso.org/iso/foreword.html.
This document was prepared jointly by Technical Committee ISO/TC 229, Nanotechnologies and Technical
Committee IEC/TC 113, Nanotechnology standardization for electrical and electronic products and systems,
and in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC
352, Nanotechnologies, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement). The draft was circulated for voting to the national bodies of both ISO and IEC.
This first edition cancels and replaces ISO/TS 21362:2018, which has been technically revised. The main
changes compared to the previous edition are as follows:
— Additional section addressing alternative and emerging methods
— Minor technical revisions to update information to the current state of the art.
— Annex A summarizing an interlaboratory comparison conducted through VAMAS

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Introduction
The capacity to isolate and analyse diverse populations of nano-objects and their agglomerates or aggregates,
often suspended in, or extracted from, complex matrices, is critical for applications ranging from materials
discovery and nanomanufacturing to regulatory oversight and environmental risk assessment. Furthermore,
the ability to characterise these analytes with minimal perturbation of their natural or native state is highly
desirable. The list of available techniques capable of achieving such objectives is relatively short, and while
all techniques have advantages and disadvantages, and no single technique is solely adequate or appropriate
for all possible applications and materials, a group of related separation techniques known collectively as
[1]
field-flow fractionation (FFF), conceptually proposed by J. Calvin Giddings in 1966 , offers many advantages
for nanotechnology applications. In FFF, the analyte, suspended in a liquid medium, is fractionated by
the application of a field (e.g. flow, centrifugal, electric, thermal-gradient, magnetic) perpendicular to the
direction of flow of the analyte and mobile phase eluting through a thin defined channel. Separation occurs
when the analyte responds to the applied field, such that populations with different response sensitivities
reach equilibrium positions (i.e. in equilibrium with diffusional forces) higher or lower in the laminar flow
streamlines perpendicular to channel flow, thus eluting differentially.
Among the FFF variants, asymmetrical flow FFF (variously abbreviated in the literature as AF4, A4F, AFFFF,
AfFFF or AsFlFFF) and centrifugal FFF (abbreviated as CF3, also called sedimentation FFF associated
with the abbreviation SdFFF), are available commercially and have been most widely adopted in the
nanotechnology field (for convenience and simplicity, the abbreviations AF4 and CF3 are used throughout
this document). AF4 is arguably the most versatile technique with respect to the wide range of applications,
materials and particle sizes to which it has been applied. Symmetrical flow FFF (fFFF), the original “flow-
[2]
based” technique as first described in 1976 , has been supplanted commercially by AF4, introduced in
[3]
1987 , due to several advantages, including a simpler channel design, the ability to visualise the sample
1)
through a transparent top channel wall, and reduced analyte band width. The theory and application of
[4]
CF3 as it is presently applied was described by Giddings and coworkers in 1974 , although a centrifugal
[5]
field-based FFF system was first developed and tested independently by Berg and Purcell in 1967 . Other
FFF field variants, such as thermal, electrical and magnetic, provide unique capabilities, but are limited in
the scope of their applications vis-à-vis nanotechnology or commercial availability.
Where FFF was once predominantly the domain of specialists, these instruments are now commonly and
increasingly utilized in government, industry and academic laboratories as part of the nano-characterization
toolbox. Two factors are driving this increase in nanotechnology utilization: maturation of commercial
instrumentation and versatility with respect to coupling a wide range of detectors to FFF systems. In the
latter case, recent developments have led to the use of highly sensitive elemental detectors (e.g. inductively
coupled plasma mass spectrometer or ICP-MS), which offer enhanced characterization and quantification for
many materials. Additionally, traditional concentration or sizing detectors, such as ultraviolet-visible (UV-
Vis) absorbance, fluorescence, multi-angle light scattering (MALS) and dynamic light scattering (DLS), yield
online data for eluting populations, and theoretically provide more accurate information than obtainable
using off-line measurements of unfractionated polydisperse systems. The measured retention time of an
eluting peak can also be used to estimate the hydrodynamic size by AF4 based on theoretical relationships
or calibration with a known size standard. CF3 has the unique capacity to rapidly separate species of the
same size but differing in density.
Although FFF based techniques have the capacity to separate and characterise analytes over an extremely
broad size range, from about 1 nm up to tens of micrometres, this document focuses primarily on materials
in the nanoscale regime and their associative structures. However, the basic underlying principles,
experimental approach, and hardware described here can be more broadly applied.
General references and further reading for FFF theory and practise, as well as AF4 and CF3 applications
to nanotechnology, are listed in the Bibliography [6]-[18]. Annex A summarizes a VAMAS interlaboratory
comparison conducted to evaluate the capacity of AF4 and CF3 techniques to separate and characterise
components of a complex multimodal mixture of analytes reproducibly and with acceptable recovery
1) Bulging of the transparent “top” wall when the channel is pressurized could alter channel volume and flow. This could
present a limitation under certain experimental conditions. Solid steel channel blocks offer an alternative that is rigid, but
lacks transparency.
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and resolution across laboratories using different commercial instrument platforms and instrument
configurations.
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DRAFT International Standard ISO/DIS 21362:2024(en)
Nanotechnologies — Analysis of nano-objects using
asymmetrical flow and centrifugal field-flow fractionation
1 Scope
This document identifies parameters and conditions, as part of an integrated measurement system,
necessary to develop and validate methods for the application of asymmetrical-flow and centrifugal
field-flow fractionation to the analysis of nano-objects and their aggregates and agglomerates dispersed
in aqueous media. In addition to constituent fractionation, analysis can include size, size distribution,
concentration and material identification using one or more suitable detectors. General guidelines and
procedures are provided for application, and minimal reporting requirements necessary to reproduce a
method and to convey critical aspects are specified.
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 80004-1, Nanotechnologies – Vocabulary — Part 1: Core vocabulary
ISO/TS 80004-6, Nanotechnologies — Vocabulary — Part 6: Nano-object characterization
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 80004-1 and ISO/TS 80004-6 and
the following, apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
3.1
nanoscale
length range approximately from 1 nm to 100 nm
[SOURCE: ISO 80004-1:2023, 3.1.1]
3.2
nano-object
discrete piece of material with one, two or three external dimensions in the nanoscale
[SOURCE: ISO 80004-1:2023, 3.1.5]
3.3
nanoparticle
nano-object with all external dimensions in the nanoscale
Note 1 to entry: If the dimensions differ significantly (typically by more than three times), terms such as nanofibre or
nanoplate are preferred to the term nanoparticle.
[SOURCE: ISO 80004-1:2023, 3.3.4]

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3.4
field-flow fractionation
FFF
separation technique where a field is applied to a liquid suspension passing along a narrow channel in order
to induce separation of the particles present in the liquid, dependent on their differing mobility under the
force exerted by the field
Note 1 to entry: The field can be, for example, gravitational, centrifugal, liquid flow, electrical or magnetic.
Note 2 to entry: Using a suitable detector after or during separation allows determination of the mean size and size
distribution of nano-object populations.
3.5
asymmetrical-flow field-flow fractionation
AF4
separation technique that uses a cross flow field applied perpendicular to the channel flow to achieve
separation based on analyte diffusion coefficient or size
Note 1 to entry: Cross flow occurs by means of a semipermeable (accumulation) wall in the channel, while cross flow is
zero at an opposing nonpermeable (depletion) wall.
Note 2 to entry: By comparison, in symmetrical flow, the cross flow enters through a permeable wall (frit) and exits
through an opposing semipermeable wall and is generated separately from the channel flow.
Note 3 to entry: Nano-objects generally fractionate by the “normal” mode, where diffusion dominates and the smallest
species elute first. In the micrometre size range, the “steric-hyperlayer” mode of fractionation is generally dominant,
with the largest species eluting first. The transition from normal to steric-hyperlayer mode can be affected by material
properties or measurement parameters, and therefore is not definitively identified; however, the transition can be
defined explicitly for a given experimental set of conditions; typically, the transition occurs over a particle size range
from about 0,5 µm to 2 µm.
Note 4 to entry: Including both normal and steric-hyperlayer modes, the technique has the capacity to separate
particles ranging in size from approximately 1 nm to about 50 µm.
3.6
centrifugal field-flow fractionation
CF3
separation technique that uses a centrifugal field applied perpendicular to a circular channel that spins
around its axis to achieve size separation of particles from roughly 10 nm to roughly 50 µm.
Note 1 to entry: Separation is governed by a combination of size and effective particle density.
Note 2 to entry: Applicable size range is dependent on and limited by the effective particle density.
3.7
channel
thin ribbon-like chamber with a parabolic flow profile required for separation
under the influence of a field applied perpendicular to the channel flow
Note 1 to entry: Channel thickness can vary and is nominally determined by a spacer insert, while fixed channels have
a predefined thickness and do not use inserts.
Note 2 to entry: In asymmetrical-flow field-flow fractionation, a trapezoidal channel is commonly used, typically with
a maximum breadth of ca. 20 mm to 25 mm and length of ca. 100 mm to 300 mm.
Note 3 to entry: In asymmetrical-flow, one channel surface (depletion wall) is solid (impermeable) and the opposing
surface (accumulation wall) consists of a semipermeable membrane on a porous frit.
Note 4 to entry: In centrifugal flow field-flow fractionation, both the inner and outer walls of the channel are solid
(non-porous) and the channel is curved. A trapezoidal channel is commonly used, typically with a breadth of 10 mm to
20 mm and length of 300 mm to 550 mm.

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3.8
spacer
thin plastic film with a cut-out that defines the thickness and lateral dimensions
of the channel
Note 1 to entry: Trapezoidal or rectangular cut-outs are most commonly used in asymmetrical-flow field-flow
fractionation.
Note 2 to entry: Typical spacer thickness used for separation of nano-objects ranges from 190 µm to 500 µm.
Note 3 to entry: Fixed channels do not use a spacer; in this case the channel shape and thickness are predefined.
3.9
channel thickness
nominal thickness as defined by the spacer or predefined in a fixed-height channel
3.10
effective channel thickness
thickness due to compressibility or swelling of the semipermeable membrane at
the accumulation wall, the effective value of which can differ from the nominal value for a given spacer and
is determined using a well-defined analyte of known diffusivity under the test conditions
Note 1 to entry: The measured effective channel thickness depends on other factors, such as interactions between the
analyte and the membrane and variability in spacer manufacturing.
3.11
accumulation wall
surface of a field-flow fractionation channel toward which sample components are forced by the applied
field acting perpendicular to the channel flow
Note 1 to entry: In asymmetrical-flow field-flow fractionation, the accumulation wall is flat and consists of a
semipermeable membrane on a porous frit substrate.
Note 2 to entry: In centrifugal field-flow fractionation, the accumulation wall is impermeable and curved, and is
located farther from the axis of rotation relative to the depletion wall. In the rare case that the particles have a lower
density than the aqueous medium, the depletion and accumulation walls are reversed.
3.12
depletion wall
surface of a field-flow fractionation channel opposite the accumulation wall, which is depleted in analyte
due to the movement of analyte toward the accumulation wall in the applied field
Note 1 to entry: In asymmetrical-flow field-flow fractionation, the depletion wall is flat and impermeable.
Note 2 to entry: In centrifugal field-flow fractionation, the depletion wall is impermeable and curved, and located
closer to the axis of rotation relative to the accumulation wall. When the effective particle density is lower than the
density of the medium, the depletion and accumulation walls are reversed.
3.13
carrier liquid
eluent
mobile phase
liquid phase used to achieve separation and transport of analytes
Note 1 to entry: The eluent or mobile phase can contain salts, surfactants, and/or other chemical constituents that are
required for optimized separation and recovery of an analyte.
Note 2 to entry: In this document, only aqueous phases are relevant, but organic solvents can also be used if equipment
and channel are compatible.
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ISO/DIS 21362:2024(en)
3.14
elution
process by which analytes in the mobile phase, or eluent, are transported through,
and exit from, the fractionation channel
Note 1 to entry: Elution begins after injection, focusing and other pre-elution steps have completed.
Note 2 to entry: Elution can occur with or without an applied field.
3.15
elution time
elapsed time after initiation of elution and excluding preliminary steps such as
injection, focusing or other transitions
Note 1 to entry: Elution and retention share the same timeline and can be use interchangeably.
Note 2 to entry: The horizontal (time) axis of a fractogram is generally expressed as elution time.
3.16
focusing
process by which, during and after sample injection a counter-
balanced flow entering from opposite ends of the channel (inlet and outlet) is applied to focus the sample
components into a thin band close to the inlet port and near the accumulation wall
Note 1 to entry: This step is necessary to minimize band broadening and to allow components to achieve an equilibrium
localization (relaxation) within the channel.
Note 2 to entry: Focusing is not used during frit-inlet injection.
3.17
relaxation
process by which the sample components assume their equilibrium state with
respect to the opposing forces of diffusion and the applied field before elution is initiated
Note 1 to entry: In flow field-flow fractionation there are two means to achieve relaxation: normal focusing relaxation
and frit inlet or hydrodynamic relaxation.
Note 2 to entry: In centrifugal field-flow fractionation, stop-flow is used to achieve relaxation.
3.18
injection flow
flow that drives the sample out of the injection loop and into the fractionation channel
Note 1 to entry: Depending on instrument design, injection can occur via a separate injection port or through the
channel inlet port.
3.19
cross flow
flow field applied perpendicular to the channel flow to achieve separation of
analytes
Note 1 to entry: In asymmetrical-flow field-flow fractionation, cross flow is created by the pressure differential across
a permeable membrane at the accumulation wall, which results in a downward force that decreases with increasing
distance from the accumulation wall.
Note 2 to entry: Cross flow is generated by using a flow controller combined with a single pump or by use of a second
dedicated pump.
3.20
channel inlet flow
mobile phase, or eluent, that enters the channel at the front end (upstream)
Note 1 to entry: In asymmetrical-flow field-flow fractionation, inlet flow is split between cross flow and channel flow
during elution.
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3.21
channel flow
parabolic laminar flow through the channel and parallel to the accumulation wall
Note 1 to entry: Channel flow is generally equivalent to the flow exiting the channel and entering the detectors under
typical experimental conditions but can differ if flow exiting the channel is split.
Note 2 to entry: In asymmetrical-flow field-flow fractionation, fluid loss through the permeable accumulation wall
leads to a linearly decreasing channel-flow velocity. This gradient can be compensated using a trapezoidal channel
design with decreasing channel breadth toward the outlet.
3.22
void volume
fluid volume defined by the channel dimensions plus the volume between the
channel exit and the first detector
3.23
void peak
peak appearing in the fractogram that corresponds to unretained material not in
equilibrium with the separation field
Note 1 to entry: The void peak travels at the average carrier fluid velocity and elutes before retained components.
Note 2 to entry: In this context, unretained means components that are not separated by the field and elute with the
void peak. Unretained has a different meaning in traditional enthalpic-based chromatographic separations.
Note 3 to entry: A void peak is generated by the mechanical disruption or change in flow conditions when elution is
initiated; in this context the void peak should ideally contain only mobile phase and small molecular species unaffected
by the applied field.
3.24
void time
time between initiation of elution and detection of the void peak defined at its maximum signal intensity
3.25
retention time
time between initiation of elution and detection of an analyte peak defined at its maximum signal intensity
Note 1 to entry: For a Gaussian peak, the maximum and peak centre are equivalent.
Note 2 to entry: Retention time and elution time represent equivalent timelines. The latter is generic, while the former
is typically used in the context of an analyte peak.
Note 3 to entry: The net retention time can be obtained by subtracting the void time from the measured peak retention
time. This equates to normalizing retention time to the elution of unretained material traveling at the mean velocity of
the channel parabolic flow.
3.26
retention parameter
dimensionless parameter equal to the ratio of the analyte zone centre-of-mass
distance (from the accumulation wall) to the channel thickness
Note 1 to entry: A measure of the strength of interaction between the applied field and the analyte.
3.27
retention ratio
ratio of the mean velocity of the analyte zone to the mean velocity of the mobile
phase in the channel during elution
Note 1 to entry: This can be calculated theoretically or determined empirically from the ratio of the elution times
associated with the void and analyte peaks and is directly related to the retention parameter.

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3.28
selectivity
measure of the ability of a method to separate analytes of different diffusion
coefficient or size
Note 1 to entry: Empirically, selectivity is calculated from the slope of a double logarithmic plot of diffusion coefficient
versus retention ratio or retention time versus analyte diameter.
Note 2 to entry: A high selectivity reflects a large change in retention time with a small variation in analyte size.
Note 3 to entry: In centrifugal field-flow fractionation, selectivity is also dependent on effective mass, but the empirical
relationship is defined in the same manner as asymmetrical-flow field-flow fractionation.
3.29
resolution factor
fractionation power
ratio of the difference in retention time to the average of the peak widths measured as the full width at half
maximum for two adjacent eluting analytes
Note 1 to entry: Measure of the degree of separation between neighbouring or overlapping peaks.
3.30
band broadening
overall dispersion or widening of an analyte band as the analyte passes through a separation system
3.31
zone broadening
broadening of the width of the sample zone during separation in the channel
3.32
normal mode (of elution)
Brownian mode
mode of elution in which diffusion is the dominant opposing force to the applied
orthogonal force (e.g., cross flow or centrifugal), resulting in an elution sequence where smaller particles
elute before larger particles
Note 1 to entry: All nanoparticles are subject to normal or Brownian mode elution, which is dominant for particle
diameters smaller than approximately 0,5 µm; nano-objects with at least one dimension greater than 0,5 µm can be
subject to steric-hyperlayer mode elution. The upper limit for normal mode elution is not well defined and depends on
both material and measurement factors.
Note 2 to entry: For centrifugal field-flow fractionation, the stated elution sequence assumes all particles have the
same density; for particles that differ in both size and density, it is possible for the elution sequence to be reversed.
3.33
steric-lift hyperlayer mode (of elution)
elution in which diffusion forces are negligible, and motion of particles due to
the applied orthogonal force (e.g., cross flow or centrifugal) is essentially impeded by resistance of the
accumulation wall itself, resulting in an elution sequence that is reversed compared to normal mode
Note 1 to entry: Steric effects occur when larger particles form layers at the accumulation wall that, on average,
project higher into the parabolic flow profile of the channel. As a result, larger particles will migrate faster than
smaller particles. Hyperlayer or lift-hyperlayer occurs when the particles form thin layers above (extended from) the
accumulation wall due to hydrodynamic effects, with larger particles more elevated than smaller particles resulting
in their faster migration. Because steric and lift-hyperlayer are closely related, forming a continuum, and produce
similar elution behaviour, they are commonly merged together.
Note 2 to entry: The lower limit for steric-hyperlayer mode elution is not well defined and can depend on both material
and measurement factors such as the channel thickness and flow rate or the applied field strength. Generally, particles
with an effective diameter greater than about 1 µm are subject to steric-hyperlayer elution, but the onset of steric-
hyperlayer effects can occur over a range from about 0,5 µm to a
...