ASTM E2490-09(2021)
(Guide)Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS)
Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS)
SIGNIFICANCE AND USE
5.1 PCS is one of the very few techniques that are able to deal with the measurement of particle size distribution in the nano-size region. This guide highlights this light scattering technique, generally applicable in the particle size range from the sub-nm region until the onset of sedimentation in the sample. The PCS technique is usually applied to slurries or suspensions of solid material in a liquid carrier. It is a first principles method (that is, calibration in the standard understanding of this word, is not involved). The measurement is hydrodynamically based and therefore provides size information in the suspending medium (typically water). Thus the hydrodynamic diameter will almost certainly differ from other size diameters isolated by other techniques and users of the PCS technique need to be aware of the distinction of the various descriptors of particle diameter before making comparisons between techniques. Notwithstanding the preceding sentence, the technique is widely applied in industry and academia as both a research and development tool and as a QC method for the characterization of submicron systems.
SCOPE
1.1 This guide deals with the measurement of particle size distribution of suspended particles, which are solely or predominantly sub-100 nm, using the photon correlation (PCS) technique. It does not provide a complete measurement methodology for any specific nanomaterial, but provides a general overview and guide as to the methodology that should be followed for good practice, along with potential pitfalls.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 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.
General Information
Relations
Standards Content (Sample)
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.
Designation: E2490 − 09 (Reapproved 2021)
Standard Guide for
Measurement of Particle Size Distribution of Nanomaterials
in Suspension by Photon Correlation Spectroscopy (PCS)
This standard is issued under the fixed designation E2490; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ISO Standards:
ISO 13320-1Particle size analysis — Laser diffraction
1.1 This guide deals with the measurement of particle size
methods — Part 1: general principles
distribution of suspended particles, which are solely or pre-
ISO 14488Particulate material — Sampling and sample
dominantly sub-100 nm, using the photon correlation (PCS)
splitting for the determination of particulate properties
technique. It does not provide a complete measurement meth-
ISO 13321Particle size analysis — Photon correlation
odology for any specific nanomaterial, but provides a general
spectroscopy
overview and guide as to the methodology that should be
followed for good practice, along with potential pitfalls.
3. Terminology
1.2 The values stated in SI units are to be regarded as
3.1 Definitions of Terms Specific to This Standard:
standard. No other units of measurement are included in this
3.1.1 Some of the definitions in 3.1 will differ slightly from
standard.
those used within other (non-particle sizing) standards (for
1.3 This standard does not purport to address all of the
example, repeatability, reproducibility). For the purposes of
safety concerns, if any, associated with its use. It is the
this guide only, we utilize the stated definitions, as they enable
responsibility of the user of this standard to establish appro-
the isolation of possible errors or differences in the measure-
priate safety, health, and environmental practices and deter-
ment to be assigned to instrumental, dispersion or sampling
mine the applicability of regulatory limitations prior to use.
variation.
1.4 This international standard was developed in accor-
3.1.2 correlation coeffıcient, n—measure of the correlation
dance with internationally recognized principles on standard-
(or similarity/comparison) between 2 signals or a signal and
ization established in the Decision on Principles for the
itself at another point in time.
Development of International Standards, Guides and Recom-
3.1.2.1 Discussion—If there is perfect correlation (the sig-
mendations issued by the World Trade Organization Technical
nals are identical), then this takes the value 1.00; with no
Barriers to Trade (TBT) Committee.
correlation then the value is zero.
3.1.3 correlogram or correlation function, n—graphicalrep-
2. Referenced Documents
resentation of the correlation coefficient over time.
2.1 ASTM Standards:
3.1.3.1 Discussion—This is typically an exponential decay.
E177Practice for Use of the Terms Precision and Bias in
3.1.4 cumulants analysis, n—mathematical fitting of the
ASTM Test Methods
correlation function as a polynomial expansion that produces
E691Practice for Conducting an Interlaboratory Study to
some estimate of the width of the particle size distribution.
Determine the Precision of a Test Method
3.1.5 diffusion coeffıcient (self or collective), n—a measure
E1617Practice for Reporting Particle Size Characterization
of the Brownian motion movement of a particle(s) in a
Data
medium.
F1877Practice for Characterization of Particles
3.1.5.1 Discussion—After measurement, the value is be
inputted into in the Stokes-Einstein equation (Eq 1, see
This guide is under the jurisdiction of ASTM Committee E56 on Nanotech-
7.2.1.2(4)). Diffusion coefficient units in photon correlation
nology and is the direct responsibility of Subcommittee E56.02 on Physical and 2
spectroscopy (PCS) measurements are typically µm /s.
Chemical Characterization.
Current edition approved Feb. 1, 2021. Published February 2021. Originally
3.1.6 Mie region, n—in this region (typically where the size
approved in 2008. Last previous edition in 2015 as E2490–09 (2015). DOI:
of the particle is greater than half the wavelength of incident
10.1520/E2490-09R21.
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 Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2490 − 09 (2021)
light), the light scattering behavior is complex and can only be 3.1.13 rotational diffusion, n—a process by which the equi-
interpreted with a more rigorous and exact (and all- librium statistical distribution of the overall orientation of
encompassing) theory. molecules or particles is maintained or restored.
3.1.6.1 Discussion—This more exact theory can be used
3.1.14 translational diffusion, n—a process by which the
instead of the Rayleigh and Rayleigh-Gans-Debye approxima-
equilibrium statistical distribution of molecules or particles in
tions described in 3.1.8 and 3.1.9. The differences between the
space is maintained or restored.
approximations and exact theory are typically small in the size
3.1.15 z-average, n—harmonic intensity weighted average
range considered by this standard. Mie theory is needed in
particlediameter(thetypeofdiameterthatisisolatedinaPCS
order to convert an intensity distribution to one based on
experiment; a harmonic-type average is usual in frequency
volume or mass.
analyses) (see 8.9).
3.1.7 polydispersityindex(PI),n—descriptorofthewidthof
3.2 Acronyms:
theparticlesizedistributionobtainedfromthesecondandthird
3.2.1 APD—avalanche photodiode detector
cumulants (see 8.3).
3.2.2 CONTIN—mathematical program for the solution of
3.1.8 Rayleigh-Gans-Debye region, n—inthisregion(stated
non-linear equations created by Stephen Provencher and ex-
to be where the diameter of the particle is up to half the
tensively used in PCS (1).
wavelength of incident light), the scattering tends to the
3.2.3 CV—coefficient of variation
forward direction, and again, an approximation can be used to
3.2.4 DLS—dynamic light scattering
describe the behavior of the particle with respect to incident
light. 3.2.5 NNLS—non-negative least squares
3.1.9 Rayleigh region, n—size limit below which the scat- 3.2.6 PCS—photon correlation spectroscopy
tering intensity is isotropic—that is, there is no angular
3.2.7 PMT—photomultiplier tube
dependence for unpolarized light.
3.2.8 QELS—quasi-elastic light scattering
3.1.9.1 Discussion—Typically, this region is stated to be
3.2.9 RGB—Rayleigh-Gans Debye
where the diameter of the particle is less than a tenth of the
wavelength of the incident light. In this region a mathematical
4. Summary of Guide
approximation can be used to predict the light-scattering
behavior. 4.1 Thisguideaddressesthetechniqueofphotoncorrelation
spectroscopy (PCS) alternatively known as dynamic light
3.1.10 repeatability, n—in PCS and other particle sizing
scattering (DLS) or quasi-elastic light scattering (QELS) used
techniques, this usually refers to the precision of repeated
for the measurement of particle size within liquid systems. To
consecutive measurements on the same group of particles and
avoidconfusion,everyusageofthetermPCSimpliesthatDLS
isnormallyexpressedasarelativestandarddeviation(RSD)or
or QELS can be used in its place.
coefficient of variation (C.V.).
3.1.10.1 Discussion—The repeatability value reflects the
5. Significance and Use
stability (instrumental, but mainly the sample) of the system
5.1 PCS is one of the very few techniques that are able to
over time. Changes in the sample could include dispersion
deal with the measurement of particle size distribution in the
(desired?) and settling.
nano-size region. This guide highlights this light scattering
3.1.11 reproducibility, n—in PCS and particle sizing this
technique, generally applicable in the particle size range from
usually refers to second and further aliquots of the same bulk
the sub-nm region until the onset of sedimentation in the
sample (and therefore is subject to the homogeneity or other-
sample. The PCS technique is usually applied to slurries or
wise of the starting material and the sampling method em-
suspensions of solid material in a liquid carrier. It is a first
ployed).
principles method (that is, calibration in the standard under-
3.1.11.1 Discussion—In a slurry system, it is often the
standing of this word, is not involved). The measurement is
largest error when repeated samples are taken. Other defini-
hydrodynamically based and therefore provides size informa-
tions of reproducibility also address the variability among
tion in the suspending medium (typically water). Thus the
single test results gathered from different laboratories when
hydrodynamic diameter will almost certainly differ from other
inter-laboratory testing is undertaken. It is to be noted that the
size diameters isolated by other techniques and users of the
same group of particles can never be measured in such a
PCS technique need to be aware of the distinction of the
system of tests and therefore reproducibility values are typi-
various descriptors of particle diameter before making com-
cally be considerably in excess of repeatability values.
parisons between techniques. Notwithstanding the preceding
3.1.12 robustness, n—a measure of the change of the sentence, the technique is widely applied in industry and
requiredparameterwithdeliberateandsystematicvariationsin academiaasbotharesearchanddevelopmenttoolandasaQC
any or all of the key parameters that influence it. method for the characterization of submicron systems.
3.1.12.1 Discussion—For example, dispersion time (ultra-
sound time and duration) almost certainly will affect the
reportedresults.VariationinpHislikelytoaffectthedegreeof
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
agglomeration and so forth. this standard.
E2490 − 09 (2021)
6. Reagents particles (of dust or contamination) falling through the mea-
surement zone (‘number fluctuations’). Ideally the form of the
6.1 In general, no reagents specific to the technique are
correlogramisanexponentialdecaytoaflatbaseline(approxi-
necessary.However,dispersingandstabilizingagentsoftenare
mating to the photon counts in the system without sample) and
requiredforaspecifictestsampleinordertopreservecolloidal
not rise again (again indicating number fluctuations in the
stability during the measurement.Asuitable diluent is used to
data). Manufacturers also provide other means of assuring the
achieve a particle concentration appropriate for the measure-
reliability of the data and is recommended that these protocols
ment. Particle size is likely to undergo change on dilution, as
are consulted, as appropriate.
theionicenvironment,withinwhichtheparticlesaredispersed,
7.1.2 Giventhenatureoftheproducedintensitydistribution
changes in nature or concentration. This is particularly notice-
and the likelihood that the size standard has been certified by
able when diluting a monodisperse latex. A latex that is
-3
electron microscopy (number distribution) care needs to be
measured as 60 nm in1×10 M NaCl can have a hydrody-
-6
exercised in direct comparison of the results. For a completely
namic diameter of over 70 nm in1×10 M NaCl (close to
monodisperse sample, (every particle identical) then the num-
deionized water). In order to minimize any changes in the
ber and intensity distributions are essentially identical. For the
system on dilution, it is common to use what is commonly
real-worldsituationwherethereissomepolydispersity(width)
called the “mother liquor”. This is the liquid in which the
to the distribution, then the number distribution is expected to
particles exist in stable form and is usually obtained by
be smaller than the produced intensity distribution; the greater
centrifuging of the suspension or making up the same ionic
the polydispersity, then the larger the differences between
nature of the dispersant liquid if knowledge of this material is
intensity, volume and number distributions. Note that verifica-
available. Many biological materials are measured in a buffer
tion of a system only demonstrates that the instrument is
(often phosphate), which confers the correct (range of) condi-
performing adequately with the prescribed standard materials.
tions of pH and ionic strength to assure stability of the system.
Practical considerations for real-world materials (especially
Instability (usually through inadequate zeta potential (2) can
‘dispersion’ if utilized or if the distribution is relatively
promote agglomeration leading to settling or sedimentation in
polydisperse) mean that the method used to measure that
a solid-liquid system or creaming in a liquid-liquid system
real-world material needs to be carefully evaluated for preci-
(emulsion). Such fundamental changes interfere with the sta-
sion (repeatability).
bilityofthesuspensionandneedtobeminimizedastheyaffect
the quality (accuracy and repeatability) of the reported mea-
7.2 Measurement:
surements.Thesearelikelytobeinvestigatedinanyrobustness
7.2.1 Introduction:
experiment.
7.2.1.1 The measurement of particle size distribution in the
nano- (sub 100 nm) region by light scattering depends on the
7. Procedure
interaction of light with matter and the random or Brownian
7.1 Verification: motion that particle exhibits in liquid medium in free suspen-
sion.There must be an inhomogeneity in the refractive indices
7.1.1 The instrument to be used in the determination should
of particle and the medium within which it exists in order for
be verified for correct performance, within pre-defined quality
light scattering to occur. Without such an inhomogeneity (for
control limits, by following protocols issued by the instrument
example, in so-called index-matched systems) there is no
manufacturer. These confirmation tests normally involve the
scattering and the particle is invisible to light and no measure-
use of one or more NIST-traceable particle size standards. In
-6
ments can be made by the PCS or any other light scattering
the sub-micron (<1×10 m) region, then these standards (for
technique.
example, NIST, Duke Scientific- now part of Thermo Fisher
Scientific)
...
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