ASTM E3427-24 Standard Guide for Measuring Intensity,Polydispersity,Size,Zeta Potential,Molecular Weight,and Concentration of Nanoparticles in Liquid Suspension Using Laser-Amplified Detection/Power Spectrum Analysis (LAD/PSA) Technology

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Designation: E3427 24
Standard Guide for
Measuring Intensity, Polydispersity, Size, Zeta Potential,
Molecular Weight, and Concentration of Nanoparticles in
Liquid Suspension Using Laser-Amplified Detection/Power
Spectrum Analysis (LAD/PSA) Technology
1
This standard is issued under the fixed designation E3427; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 The technology, laser-amplified detection/power spec-
trum analysis (LAD/PSA), is available in three different
platforms, which will be designated as Platforms A, B, and C.
1.1.1 Platform A—This is a solid-state probe configuration
that serves as the optical bench in each of the platforms. It
consists of an optical fiber coupler with a y-beam splitter that
directs the scattered light signal from the nanoparticles at 180°
back to a photodiode detector. The sensing end of the probe can
be immersed in a suspension or positioned to measure one drop
of a sample on top of the sensing surface.
1.1.2 Platform B—The same probe is mounted in a case,
positioned horizontally, to detect the signal from either a
disposable or permanent cuvette.
1.1.3 Platform C—Two probes are mounted in a case,
horizontally, at opposite sides of a permanent sample cell. Both
size distribution and zeta potential can be measured in this
configuration.
1.2 The laser beam travelling through the probe measuring
the scattered light from the sample of nanoparticles, in all three
platforms, is partially reflected back to the same photodiode
detector, and the high optical power of the laser is added to the
low optical power of the scattered light signal. The interference
(mixing or beating) of those two signals is known as hetero-
dyne beating. The resulting high-power detected signal pro-
vides the highest signal-to-noise ratio among dynamic light-
scattering (DLS) technologies.
1.3 This combined, amplified, optical signal is converted
with a Fast Fourier transform (FFT) into a frequency power
spectrum, then into a logarithmic power spectrum that is
deconvolved into number and volume size distributions. The
mean intensity, polydispersity, number and volume size
distributions, concentration, and molecular weight can be
reported in all platforms, plus zeta potential on Platform C.
1.4 This technology is capable of measuring nanoparticles
in a size range from 2.0 nanometres (nm) to 10 micrometres
(µm), at concentrations in a suspending liquid medium up to
40 % cc ⁄mL for all parameters given in 1.3.
1.5 Units—The values stated in SI units are to be regarded
as the standard. No other units of measurement are included in
this standard.
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
E1817 Practice for Controlling Quality of Radiological Ex-
amination by Using Representative Quality Indicators
(RQIs)
E2456 Terminology Relating to Nanotechnology
E2490 Guide for Measurement of Particle Size Distribution
of Nanomaterials in Suspension by Photon Correlation
Spectroscopy (PCS)
E2834 Guide for Measurement of Particle Size Distribution
of Nanomaterials in Suspension by Nanoparticle Tracking
Analysis (NTA)
E3247 Test Method for Measuring the Size of Nanoparticles
1
This guide is under the jurisdiction of ASTM Committee E29 on Particle and
Spray Characterization and is the direct responsibility of Subcommittee E29.02 on
Non-Sieving Methods.
Current edition approved Feb. 1, 2024. Published February 2024. DOI: 10.1520/
E3427-24.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
1
in Aqueous Media Using Dynamic Light Scattering
2.2 ISO Standards:
3
ISO 14488 Particulate Material—Sampling and Sample
Splitting for the Determination of Particulate Properties
ISO 22412 Particle Size Analysis—Dynamic Light Scatter-
ing (DLS)
3. Terminology
3.1 Definitions—For definitions of terms pertaining to this
guide not otherwise listed in 3.2, reference should be made to
ISO 22412, Guides E2490 and E2834, and Test Method E3247.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 deconvolution, n—iterative computational technique
that calculates an estimate of the answer to a problem.
3.2.1.1 Discussion—The error between the problem and the
estimate is calculated and the estimate is refined. The process
is repeated until the error is minimized to a desired minimal
value.
3.2.2 Fast Fourier transform, FFT, n—algorithm that con-
verts a signal from the amplitude/time domain to the
amplitude/frequency domain.
3.2.3 fiber optic coupler, n—fiber optic device capable of
combining two or more inputs into a single output and also
dividing a single input into two or more outputs.
3.2.4 heterodyne (reference beating), adj—heterodyne de-
tection is the mixing of scattered light from nanoparticles with
a reference light beam from the same source, which is a laser
in this technology (refer to heterodyne diagram in Fig. 1).
3.2.4.1 Discussion—Sinusoidal electromagnetic waves are
generated, as related to dynamic light scattering (DLS), from
each nanoparticle in the scattering region of the incident laser
signal. The intensity of the scattered light from each nanopar-
ticle is added to the intensity of the laser reference beam of
much greater optical power than the optical power of the
scattered light from the nanoparticles.
3.2.5 homodyne (self-beating), adj—sinusoidal electromag-
netic waves are generated, as related to DLS, from all the
different pairs of nanoparticles in the scattering region of the
incident laser signal representing the sum of the scattered light
intensity for each pair added together (refer to homodyne
diagram in Fig. 1).
3.2.6 y-splitter, n—location in a fiber optic coupler where a
single beam is divided into two beams and where two beams
are combined into one.
3.3 Acronyms:
3.3.1 CWV—constant water volume
3.3.2 DI—deionized
3.3.3 DLS—dynamic light scattering
3.3.4 FPS—frequency power spectrum
3.3.5 IPA—isopropyl alcohol
3.3.6 LAD/PSA—laser-amplified detection/power spectrum
analysis
3.3.7 LI—loading index
3.3.8 MI—mean intensity
3.3.9 MW—molecular weight
3.3.10 NTA—nanoparticle tracking analysis
3.3.11 PCS—photon correlation spectroscopy
3.3.12 PI—polydispersity index
3.3.13 PSA—power spectrum analysis
3.3.14 PSD—power spectrum distribution
3.3.15 QLS—quasi-elastic light scattering
3.3.16 RI—refractive index
3.3.17 RRI—relative refractive index
3
Available from International Organization for Standardization (ISO), ISO
Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, https://www.iso.org.
FIG. 1 Comparison Diagrams of Homodyne and Heterodyne Detection
E3427 − 24
2
4. Significance and Use
4.1 In this guide, the conditions, measurement apparatus,
and procedures for measuring several characteristics of nan-
oparticle properties on three different instrument platforms
using laser-amplified detection/power spectrum analysis
(LAD/PSA) technology are described. This is a more recently
developed technology, commercialized in 1990, than the older
technology known as either photon correlation spectroscopy
(PCS) or quasi-elastic light scattering (QLS)—those titles are
interchangeable—developed first in 1961. Nanoparticle track-
ing analysis (NTA) is the most recent DLS technology to be
commercialized. All three of these technologies fall under the
broader category of DLS, based on the “dynamic” movement
of the measured nanoparticles under Brownian motion.
4.2 DLS in the lower end of the nanometre size range
becomes progressively more difficult as the particle optical
scattering coefficients drop sharply, reducing the scattered light
intensity. The advantage of the heterodyne detection mode over
the homodyne detection mode, especially at the low end of the
nanometre range, will be explained.
4.3 The LAD/PSA technology will be described and the
major differences between it and the PCS-QLS and NTA
technologies will be made clear. For thorough discussions of
PCS-QLS, refer to Guide E2490, Test Method E3247, and ISO
22412 Annex Section A.1. For a thorough discussion of
nanoparticle tracking analysis (NTA), refer to Guide E2834.
For detailed information on laser-amplified detection/
frequency power spectrum (LAD/FPS) technology, refer to
ISO 22412 Annex Section A.2. General information on particle
characterization practices can be found in Practice E1817, and
nanotechnology terminology is given in Terminology E2456.
Detailed information on sampling for particle characterization
can be found in ISO 14488.
5. Procedure
5.1 Laser-Amplified Detection (LAD)—In this guide, the
differences among three different instrument Platforms, A, B,
and C, will be made clear using this type of detection and
subsequent analysis. This type of particle measurement tech-
nology is used to measure, and report mean intensity, polydis-
persity index (PI), number and volume size distributions,
concentration, molecular weight, and zeta potential of nanopar-
ticles in a liquid undergoing Brownian motion. Brownian
motion refers to the random movement displayed by small
particles that are suspended in fluids being struck by the
molecules in solution as a function of the temperature and
viscosity of the fluid. This motion is a result of the collisions of
the particles with the random movement of the molecules in the
fluid. LAD uses heterodyne detection. PCS-QLS uses homo-
dyne detection. PCS-QLS uses time-based autocorrelation to
process the detected homodyne signal. LAD/PSA uses power
spectrum analysis to process the detected heterodyne signal.
5.1.1 Platform A—This is a solid-state probe configuration
that serves as the optical bench in all three platforms. This
platform measures all parameters mentioned in 5.1 except zeta
potential. It consists of an optical fiber coupler with a y-splitter
enclosed in a stainless-steel cylindrical casing (see Fig. 2). A
laser signal travels through a Grin lens that maintains the
spatial separation of the nanoparticles and then through a
sapphire window that has a high reflectance. The nanoparticles
scatter light back to the probe window at 180° at frequencies in
the thousands of Hertz (audible) range compared to the
constant laser reference frequency in the range of about 14
Terahertz (4.61 × 10
14
Hz). Computers do not scan at a high
enough speed to detect the frequency shifts at these
frequencies, so the high-frequency (laser) component is sub-
tracted from the combined frequencies and that allows the
successful detection of the low (scatter) frequency shift signals.
The interference of a high-power, unchanging, reference signal
(laser beam) with a lower-power, changing, measured signal
(the scattered light) is heterodyne detection. These two sinu-
soidal wave forms interfere with each other, resulting in a beat
signal with an optical power that is the sum of the weak
scattered light signal and the high power of the laser signal. As
light scatters from the moving nanoparticles, this motion
imparts a randomness to the phase of the scattered light, such
that when the scattered light from each particle is added to the
constant frequency laser reference beam, there will be a
changing constructive or destructive interference. This leads to
time-dependent fluctuations in the intensity of the scattered
light. When no reference signal is used, the scattered light from
all pairs of particles interfering with each other is summed and
so is the homodyne detection with a much lower optical power
FIG. 2 LAD/PSA Heterodyne Detection Probe
E3427 − 24
3
compared to that for heterodyne detection. The two optical
fibers that couple at the y-splitter (laser beam and scattered
light signal) are connected to a case containing the laser and
detector electronics.
4
5.1.1.1 Nanoparticles that have a radius less than approxi-
mately one tenth the wavelength of the radiation undergo
Rayleigh scattering. In the Rayleigh scattering range, the
homodyne-detected signal level drops off by diameter, d, at
10
6
. The heterodyne-detected signal power drops off by only
10
3
. The pairs of scattered light detected in the homodyne
mode are the sum of two low optical power signals (i
scat
)
2
. See
Fig. 2 for diagrams of both the homodyne and heterodyne
detection methods. The signal detected in the heterodyne mode
is the sum of the mixed scattered light signal and the
high-power reference signal, (i
ref0
)×(i
scat
). The signal level for
the controlled reference mode can, thus, be made to be orders
of magnitude larger than the homodyne mode by providing a
high level of reference signal intensity and signal-to-noise
ratio.
5.1.1.2 The probe can be attached to the outside of the case
at the end of a rotational clamp, which is also adjustable up and
down. A variety of sample containers, such as beakers,
cuvettes, and test tubes, can be placed below the probe, and the
probe can be lowered into the sample, handheld, or attached to
the clamp. The clamp can also be rotated 180° so that the
sensing end of the probe is pointed upwards, and a drop of
sample as small as 2 µL can be deposited on the sapphire
window to make the measurement. This is the desired orien-
tation when the samples are small or expensive, or both. The
high power of the laser amplified detection signal allows
measurement of particle concentrations up to 40 mg ⁄mL,
which includes samples that are obtained already prepared,
such as inks. paints, pigments, and others, without diluting the
samples.
5
5.1.2 Platform B—The optical bench/probe described and
shown in Fig. 2 is mounted horizontally in a case with the
sensing end of the detector placed against a disposable or
permanent cuvette containing the sample. This platform mea-
sures all parameters mentioned previously except zeta poten-
tial.
5.1.3 Platform C—Two probes are placed such that the
windows of the probes are within the walls, on opposite sides,
of a permanent sample cell. This platform measures all
parameters in 5.1. It is the only platform that also measures
zeta potential (Fig. 3).
5.1.3.1 Zeta Potential Measurement—When measuring size,
only one of the probes is activated and functions as it does in
the other platforms. When measuring zeta potential, both
probes are activated. The measurement of zeta potential takes
advantage of the same power spectrum analysis (PSA) used for
measuring size. The backscatter and laser-amplified (hetero-
dyne) detection signals are collected as in the size
measurement, and the rapid sequencing of applied electric
fields prevents electroosmosis. The optical probe surfaces are
coated to provide electrical contact with the sample. One probe
determines the polarity of the particle charge and the other
measures the mobility of the particles in an electric field.
Polarity is measured in a pulsed electric field, while mobility is
measured in a high-frequency sine wave electric field excita-
tion. From the power spectrum distribution (PSD), the loading
index (LI) is calculated as the sum of the amplitudes of all
logarithmic frequency channels (refer to 5.2, Power Spectrum
Analysis) and depends on the particle concentration. The LI is
proportional to the number of particles in each channel. LI
values provide a single number for total scattering that can be
used to determine particle mobility in microns/seconds/volt/
centimetre and particle polarity as 6, positive or negative, and
volt/centimetre and particle polarity as 6, positive or negative.
Measuring mobility and zeta potential begins by measuring the
PSD and determining the LI with the excitation off. Then, the
PSD is measured with the high-frequency sine wave on, and a
ratio is taken. Polarity is determined by measuring the LI
before and after pulsed DC excitation. A ratio of LI after the
excitation divided by LI before excitation of less than one is a
positive polarity (concentration decreasing) and a ratio greater
than one is negative (concentration increasing) for a positively
charged probe surface (refer to Fig. 3).
5.1.3.2 Zeta potential dependence on concentration is an
important factor in getting correct measurements. The formu-
lation of complex and commercial mixtures highly loaded with
solids, such as paints, inks, pharmaceuticals, herbicides, and
composite plastics should not be diluted when measuring their
zeta potential. These samples are prepared with the proper
ionic or non-ionic surfactants to achieve an ionic strength that
provides excellent stability and prevents agglomeration. Dilu-
tion with any liquid other than that used in their preparation can
lower the ionic strength of the suspension, causing agglomera-
tion and changing the zeta potential of the original suspension.
4
The (U.S. Patent No. 5094532, Mar. 1992) is covered by a patent. Interested
parties are invited to submit information regarding the identification of an
alternative(s) to this patented item to the ASTM International Headquarters. Your
comments will receive careful consideration at a meeting of the responsible
technical committee, which you may attend.
5
Trainer, M. N., Freud, P. J., and Leonardo, E. M., “High-concentration
submicron particle size distribution by dynamic light scattering,” American
Laboratory, Vol 24, July 1992, p. 34.
FIG. 3 Schematic of Zeta Potential Cell/Probes Setup
E3427 − 24
4
摘要:

ASTM E3427-2024 Standard Guide for Measuring Intensity,Polydispersity,Size,Zeta Potential,Molecular Weight,and Concentration of Nanoparticles in Liquid Suspension Using Laser-Amplified Detection/Power Spectrum Analysis (LAD/PSA) Technology

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