1、Designation: E2834 12Standard Guide forMeasurement of Particle Size Distribution of Nanomaterialsin Suspension by Nanoparticle Tracking Analysis (NTA)1This standard is issued under the fixed designation E2834; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide deals with the measurement of particle sizedistribution of suspended
3、 particles, from 10 nm to the onset ofsedimentation, sample dependent, using the nanoparticle track-ing analysis (NTA) technique. It does not provide a completemeasurement methodology for any specific nanomaterial, butprovides a general overview and guide as to the methodologythat should be followed
4、 for good practice, along with potentialpitfalls.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibili
5、ty of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C322 Practice for Sampling Ceramic Whiteware ClaysE456 Terminology Relating to Quality and Statisti
6、csE1617 Practice for Reporting Particle Size CharacterizationDataE2490 Guide for Measurement of Particle Size Distributionof Nanomaterials in Suspension by Photon CorrelationSpectroscopy (PCS)2.2 ISO Standards:3ISO 13320 Particle Size AnalysisLaser Diffraction Meth-odsISO 13321 Particle Size Analysi
7、sPhoton CorrelationSpectroscopyISO 14488 Particulate MaterialsSampling And SampleSplitting for the Determination of Particulate PropertiesISO 22412 Particle Size AnalysisDynamic Light Scatter-ing (DLS)3. Terminology3.1 Definitions:3.1.1 diffusion coeffcient, na measure to characterize therate a part
8、icular molecule or particle moves in a particularmedium when driven by random thermal agitation (Brownianmotion).3.1.1.1 DiscussionAfter measurement, the value is to beinputted into the Stokes-Einstein equation (Eq 1, see7.2.1.2(3). Diffusion coefficient units in nanoparticle trackinganalysis (NTA)
9、measurements are typically cm2/s, rather thanthe correct SI units of m2/s.3.1.2 repeatability, nin NTA and other particle sizingtechniques, this usually refers to a measure of the precision ofrepeated consecutive measurements on the same group ofparticles under identical conditions and is normally e
10、xpressedas a relative standard deviation (RSD) or coefficient of varia-tion (CV).3.1.2.1 DiscussionThe repeatability value reflects the sta-bility (instrumental, but mainly the sample) of the system overtime. Changes in the sample could include dispersion, aggre-gation and settling.3.1.3 reproducibi
11、lity, nin NTA and particle sizing thisusually refers to a measure of the deviation of the resultsobtained from the first aliquot to that obtained for the secondand further aliquots of the same bulk sample (and therefore issubject to the homogeneity or heterogeneity of the startingmaterial and the sa
12、mpling method employed). Normally ex-pressed as a relative standard deviation (RSD) or coefficient ofvariation (CV).3.1.3.1 DiscussionIn a heterogenous and polydisperse(for example, slurry) system, it is often the largest error whenrepeated samples are taken. Other definitions of reproducibilityalso
13、 address the variability among single test results gatheredfrom different laboratories when inter-laboratory testing is1This guide is under the jurisdiction of ASTM Committee E56 on Nanotech-nology and is the direct responsibility of Subcommittee E56.02 on Characterization:Physical, Chemical, and To
14、xicological Properties.Current edition approved April 1, 2012. Published May 2012. DOI: 10.1520/E2834-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standar
15、ds Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.undertaken, or
16、 operator-to-operator, instrument-to-instrument,location-to-location, or even day-to-day. It is to be noted thatthe same group of particles can never be measured in such asystem of tests and therefore reproducibility values maytypically be considerably in excess of repeatability values.3.1.4 robustn
17、ess, na measure of the change of the re-quired parameter with deliberate and systematic variations inany or all of the key parameters that influence it.3.1.4.1 DiscussionFor example, dispersion energy input(that is, ultrasound power and duration) almost certainly willaffect the reported results. Var
18、iation in pH is likely to affect thedegree of agglomeration and so forth. A useful discussion ofrobustness experiment considerations is found in the ICHValidation of Analytical Procedures Q2(R1) Guideline (1).43.1.5 rotational diffusion, na process by which the equi-librium statistical distribution
19、of the overall orientation ofmolecules or particles is maintained or restored.3.1.6 translational diffusion, na process by which theequilibrium statistical distribution of molecules or particles inspace is maintained or restored.3.1.7 visualization, nas it relates to the NTA technique,the particles
20、themselves are not imaged, being below thediffraction limit. Each particle acts as a point scatterer, meaningthat the imaging system only sees the scattered light from theparticle. This allows the position of each particle to beidentified and followed with respect to time. See 7.2.3.1.7.1 Discussion
21、The intensity and shape of the scat-tered light pattern for each particle may vary, and someadditional information may be obtained from these differences,at least qualitatively, but is outside the scope of this guide.3.1.8 percentile, na statistical measure of the distributionof sizes. The size belo
22、w which a certain percent of thedistribution falls. For example, the 10th percentile is the sizebelow which 10 percent of the particles may be found.Expressed in ISO form as x10,x50,x90, and also commonlyexpressed as D10, D50, D90. The 50th percentile is themedian.3.1.9 coeffcient of variation, nin
23、statistics, a normalizedmeasure of dispersion of a distribution. Defined as the standarddeviation divided by the mean value. (Note: CV = SD/Mean)3.1.10 relative standard deviation, nin statistics, the ab-solute value of the coefficient of variation, expressed as apercentage. (Note: RSD = 100SD/Mean)
24、NOTE 1Other common statistical measures are defined in Terminol-ogy E456.3.2 Acronyms:3.2.1 CVcoefficient of variation3.2.2 CCDcharge-coupled device3.2.3 CMOScomplementary metaloxidesemiconductor3.2.4 DLSdynamic light scattering3.2.5 EMCCDelectron-multiplying charge-coupled de-vice3.2.6 NTAnanoparti
25、cle tracking analysis3.2.7 PCSphoton correlation spectroscopy3.2.8 RSDrelative standard deviation4. Summary of Guide4.1 Nanoparticle tracking analysis (NTA) is a method forthe direct and real-time visualization and analysis of nanopar-ticles in liquids. Particles in suspension are illuminated with a
26、focused laser beam. Light scattered from each particle isvisible through magnifying optics fitted to a digital camerasuch as a CCD. The software analyzes the video stream fromthe camera, identifying and tracking the motion of each particlewith time. Because each particle in the field of view is bein
27、gsimultaneously but separately tracked and analyzed, the par-ticle size distribution profile obtained by NTA is a directnumber-based distribution.4.2 The laser beam is focused such that only particles in thefocal plane of the magnifying optics are illuminated. Particlesout of the focal plane are not
28、 illuminated and at the size rangeunder discussion are not visible to the camera. This yields ahigh signal to noise image, allowing particles as small as 10 nmto be visualized, depending on sample material. While outsidethe scope of this document, the technique is generally able tomeasure particles
29、as large as approximately 1 m.4.3 The average distance each particle moves in the image isautomatically calculated by the software. From this value, theparticle diffusion coefficient can be obtained and through theuse of the Stokes-Einstein equation, particle size can bedetermined.4.4 This Guide dis
30、cusses the scientific basis for the tech-nique, size limits, concentration ranges, sampling and samplepreparation considerations, condition and analysis selection,data interpretation and comparison to other complementarytechniques.5. Significance and Use5.1 NTA is one of the very few techniques that
31、 are able todeal with the measurement of particle size distribution in thenano-size region. This Guide describes the NTA technique fordirect visualization and measurement of Brownian motion,generally applicable in the particle size range from severalnanometers until the onset of sedimentation in the
32、 sample. TheNTA technique is usually applied to dilute suspensions of solidmaterial in a liquid carrier. It is a first principles method (thatis, calibration in the standard understanding of this word, is notinvolved). The measurement is hydrodynamically based andtherefore provides size information
33、in the suspending medium(typically water). Thus the hydrodynamic diameter will almostcertainly differ from size diameters determined by othertechniques and users of the NTA technique need to be aware ofthe distinction of the various descriptors of particle diameterbefore making comparisons between t
34、echniques (see 8.7).Notwithstanding the preceding sentence, the technique isroutinely applied in industry and academia as both a researchand development tool and as a QC method for the character-ization of submicron systems.6. Reagents6.1 In general, no reagents specific to the technique arenecessar
35、y. However, dispersing and stabilizing agents often are4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.E2834 122required for a specific test sample in order to preserve colloidalstability during the measurement. A suitable diluent is used toachieve a p
36、article concentration appropriate for the measure-ment. The apparent hydrodynamic size or diffusion coefficientmay undergo change on dilution, as the ionic environment,within which the particles are dispersed, changes in nature orconcentration. This is particularly noticeable when diluting amonodisp
37、erse latex. A latex that is measured as 60 nm in 1 310-3M NaCl can have a hydrodynamic diameter of over 70 nmin 1 3 10-6M NaCl (close to deionized water).6.2 In order to minimize any changes in the system ondilution, it is common to use the “mother liquor”. This is theliquid in which the particles e
38、xist in stable form and is usuallyobtained by centrifuging of the suspension or making up thesame ionic composition of the dispersant liquid if knowledgeof these components is available. Many biological materialsare measured in a buffer (often phosphate buffered saline),which confers the correct (ra
39、nge of) conditions of pH and ionicstrength to assure stability of the system. Instability (usuallythrough inadequate zeta potentialsee (2) can promote ag-glomeration leading to settling or sedimentation in a solid-liquid system or creaming in a liquid-liquid system (emulsion).Such fundamental change
40、s interfere with the stability of thesuspension and need to be minimized as they affect the quality(accuracy and repeatability) of the reported measurements.These should be investigated in a robustness experiment.7. Procedure7.1 Verification:7.1.1 The instrument to be used in the measurement shouldb
41、e verified for correct performance, within pre-defined qualitycontrol limits, by following protocols issued by the instrumentmanufacturer. These confirmation tests normally involve theuse of one or more NIST-traceable spherical particle sizestandards. In the sub-micron (10 %), care must be exercised
42、 to ensure that theappropriate methods and conditions are selected to ensurereliable results. Analysis time, image capture settings, andsample concentration are variables that need to be considered.8.8 Conversion of the Concentration Distribution to OtherParticle Size Distributions:8.8.1 With any te
43、chnique, the most reliable results are thosereported in that techniques natural format. Conversion to otherdistribution bases may be mathematically valid, but the as-sumptions in obtaining this derived information need to becarefully understood and the implications of reporting thisinformation also
44、carefully evaluated. Small changes in col-lected data can give rise to enormous changes in derived resultand as such treat any derived result with caution and skepti-cism. To convert from concentration to volume distributionwould involve the manipulation of perfect noise-free experi-mental data. The
45、 wider the initial distribution the more seriousare the potential errors in the conversion.8.8.2 Notwithstanding the above caveats and cautions, con-version to a volume-weighted distribution can often provide anindication of the relative importance (prominence) of two ormore reported peaks. A common
46、 situation is to see an appar-ently dominant small-size peak virtually disappearing and alow-intensity larger-sized peak becoming the primary modeafter conversion to volume weighting.9. Report9.1 See Practice E1617.9.2 As a minimum the following need reporting in additionto graphical and tabular inf
47、ormation:9.2.1 The instrument type and manufacturer and serialnumber. Version of software employed.9.2.2 Date and results of the last verification. Details of thetraceability of the standards employed.9.2.3 Date of measurement together with analysts nameand affiliation.9.2.4 Details of the sample in
48、cluding chemical composition.Shape information if obtained by electron microscopy oratomic force microscopy is helpful.9.2.5 Details of the dispersion conditions (concentration ofmaterial, liquid used, ultrasound time, frequency and power,surfactants and stabilizing agents, if used, and their concen
49、tra-tion) and evidence that full dispersion or primary particle sizehas been reached.9.2.6 Measurement conditionstime of measurement,wavelength of laser, stabilization period prior to measurement,temperature. Number of measurements.9.2.7 Minimum of 3 replicate consecutive measurements.This demonstrates the stability of the material (especially) andthe instrument during the duration of the measurements. Theuse of a relative standard deviation (RSD) or coefficient ofvariation (CV) is highly recommended.9.2.8 Minimum of 3 separate aliquots/sample
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