E56.02 - Physical and Chemical Characterization

SIGNIFICANCE AND USE
5.1 Liposomal formulations for the treatment of cancer and other diseases are the most common form of nanotechnology-enabled drug products submitted for market approval and in clinical application at the present time. The accurate characterization of their physical-chemical properties is critical to support the development and assessment of such products (2). In particular, size, size distribution, shape, and physical stability are key properties (among others) that have been widely identified as critical quality attributes (CQAs) for liposomal drug products.  
5.1.1 Asymmetrical-flow field-flow fractionation (AF4) is a chromatographic-like technique that uses hydrodynamic forces to gently separate analytes into their component populations according to size and diffusivity (3 and 4). The fractionated sample then passes through one or more online detectors chosen specifically for the application requirements. The combination of low-shear separation, tolerance for complex matrices, and exceptionally broad size range make AF4 a technique of choice for application to nanotechnology-enabled drug products such as liposomes (13, 5-9).  
5.1.2 Multi-detector AF4 is suitable for research and development, manufacturing quality control, product stability/shelf-life testing and regulatory assessments.  
5.1.3 There are multiple assumptions inherent in the application of MD-AF4, including the appropriateness of models used to interpret online light scattering data and the compatibility of the analyte and matrix with the membrane that forms the surface of the accumulation wall in the fractionation channel. Other assumptions are detector or analyte specific.  
5.2 Chemical components of the mobile phase must not induce agglomeration of liposomes or otherwise significantly alter their physical properties.  
5.3 Discretion should be used in the interpretation of size data obtained by different scattering detectors using different scattering models and modes of analysis.  
5.4 ...
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1.1 This test method describes a measurement procedure to reproducibly separate component size populations present within liposomal drug formulations and to characterize their associated size and size distribution. The method can also yield information on the shape and physical stability of the liposomes and is applicable to measurements in the presence of serum proteins. Fractions can be collected for off-line analysis using various techniques not specified in this test method.  
1.2 This test method applies to uni-lamellar and multi-lamellar liposomes that are designed for drug delivery and which are dispersed in a native solution that is aqueous in nature. The method is generally applicable over a particle size range (radius) of approximately 10 nm to 250 nm, and for injected lipid mass from 20 µg to 200 µg.  
1.3 This test method is based on the multi-detector asymmetrical-flow field-flow fractionation (MD-AF4) technique as configured on a typical commercial instrument platform with online detectors such as multi-angle (static) light scattering (MALS), dynamic light scattering (DLS), ultraviolet-visible (UV-Vis) absorbance, and differential refractive index (dRI) (1).2  
1.4 This method does not address liposome composition. Refer to Test Methods E3297, E3323, or E3324 for lipid quantification.  
1.5 Units—The values stated in SI units are to be regarded as standard. Where appropriate, cgs units are given in addition to SI.  
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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of In...

SIGNIFICANCE AND USE
5.1 As AFM measurement technology has matured and proliferated, the technique has been widely adopted by the nanotechnology research and development community to the extent that it is now considered an indispensible tool for visualizing and quantifying structures on the nanoscale. Whether used as a stand-alone method or to complement other dimensional measurement methods, AFM is now a firmly established component of the nanoparticle measurement tool box. International standards for AFM-based determination of nanoparticle size are nonexistent as of the drafting of this guide. Therefore, this standard aims to provide practical and metrological guidance for the application of AFM to measure the size of substrate-supported nanoparticles based on maximum displacement as the probe is rastered across the particle surface to create a line profile.
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1.1 The purpose of this document is to provide guidance on the quantitative application of atomic force microscopy (AFM) to determine the size of nanoparticles2 deposited in dry form on flat substrates using height (z-displacement) measurement. Unlike electron microscopy, which provides a two-dimensional projection or a two-dimensional image of a sample, AFM provides a three-dimensional surface profile. While the lateral dimensions are influenced by the shape of the probe, displacement measurements can provide the height of nanoparticles with a high degree of accuracy and precision. If the particles are assumed to be spherical, the height measurement corresponds to the diameter of the particle. In this guide, procedures are described for dispersing gold nanoparticles on various surfaces such that they are suitable for imaging and height measurement via intermittent contact mode AFM. Generic procedures for AFM calibration and operation to make such measurements are then discussed. Finally, procedures for data analysis and reporting are addressed. The nanoparticles used to exemplify these procedures are National Institute of Standards and Technology (NIST) reference materials containing citrate-stabilized negatively charged gold nanoparticles in an aqueous solution.  
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.

SIGNIFICANCE AND USE
5.1 Cryo-TEM is a technique used to record high resolution images of samples that are frozen and embedded in a thin layer of vitrified, amorphous ice (2-5). Because vitrification occurs so rapidly, the resultant specimen is almost instantly frozen, yielding a very accurate representation of the specimen at the moment of freezing, without the distortions typically associated with air drying delicate wet samples. Once frozen, images of the specimen are recorded at low temperature using a specially designed electron microscope equipped with a cryo-holder capable of operating under low dose conditions in order to prevent beam induced structural damage to the specimen. The cryo-TEM technique is the consensus choice to directly observe, analyze and accurately measure liposomes suspended in aqueous solutions. Fig. 1 illustrates this by comparing an electron micrograph from an air-dried negatively stained liposomal preparation with an electron micrograph of the same solution imaged by cryo-TEM.
FIG. 1 Left—An Electron Micrograph of an Air-Dried Liposomal Preparation that has been Negatively Stained with 2 % Uranyl Acetate for Contrast; Right—An Electron Micrograph of the Same Liposomal Preparation Prepared as a Frozen Vitrified Specimen for Cryo-TEM
Note 1: Both images are shown to the same scale; scale bar is 200 nm.  
5.1.1 Fig. 1 demonstrates that liposomes may become distorted and are difficult to measure and analyze when they are air-dried, while the same liposomal preparation is clearly easier to analyze when the specimen is near-instantly preserved by vitrification.  
5.1.2 Cryo-TEM involves applying a small volume of sample to a specially prepared holey, ultra-thin or continuous carbon grid suspended in a cryo-TEM plunger over a cup of liquid ethane cooled in a container filled with liquid nitrogen (2, 3). These grids can be purchased or prepared in the laboratory using a carbon evaporator with glow discharge capabilities. Once the sample has wet the surface o...
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1.1 This practice covers procedures for vitrifying and recording images of a suspension of liposomes with a cryo-transmission electron microscope (cryo-TEM) for the purpose of evaluating their shape, size distribution and lamellarity for quality assessment. The sample is vitrified in liquid ethane onto specially prepared holey, ultra-thin, or continuous carbon TEM grids, and imaged in a cryo-holder placed in a cryo-TEM.  
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.

SIGNIFICANCE AND USE
5.1 A tiered strategy for characterization of nanoparticle properties is necessary to draw meaningful conclusions concerning dose-response relationships observed during inhalation toxicology experiments. This tiered strategy includes characterization of nanoparticles as produced (that is, measured as the bulk material sold by the supplier) and as administered (that is, measured at the point of delivery to a test subject) (Oberdorster et al. (6)).  
5.2 Test Methods B922 and C1274 and ISO 9277 and ISO 18757 exist for determination of the as produced surface area of bulk metal and metal oxide powders. During the delivery of nanoparticles in inhalation exposure chambers, the material properties may undergo change and therefore have properties that differ from the material as produced. This test method describes the determination of the as administered surface area of airborne metal oxide nanoparticles in inhalation exposure chambers for inhalation toxicology studies.
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1.1 This test method covers determination of surface area of airborne metal oxide nanoparticles in inhalation exposure chambers for inhalation toxicology studies. Surface area may be measured by gas adsorption methods using adsorbates such as nitrogen, krypton, and argon (Brunauer et al. (1),2 Anderson (2), Gregg and Sing (3)) or by ion attachment and mobility-based methods (Ku and Maynard (4)). This test method is specific to the measurement of surface area by gas adsorption by krypton gas adsorption. The test method permits the use of any modern commercial krypton adsorption instruments but strictly defines the sample collection, outgassing, and analysis procedures for metal and metal oxide nanoparticles. Use of krypton is required due to the low overall surface area of particle-laden samples and the need to accurately measure the background surface area of the filter used for sample collection. Instrument-reported values of surface area based on the multipoint Brunauer, Emmett and Teller (BET) equation (Brunauer et al. (1), Anderson (2), Gregg and Sing (3)) are used to calculate surface area of airborne nanoparticles collected on a filter.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. State all numerical values in terms of SI units unless specific instrumentation software reports surface area using alternate units.  
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.

SIGNIFICANCE AND USE
5.1 NTA 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 describes the NTA technique for direct visualization and measurement of Brownian motion, generally applicable in the particle size range from several nanometers until the onset of sedimentation in the sample. The NTA technique is usually applied to dilute 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 size diameters determined by other techniques and users of the NTA technique need to be aware of the distinction of the various descriptors of particle diameter before making comparisons between techniques (see 8.7). Notwithstanding the preceding sentence, the technique is routinely applied in industry and academia as both a research and development tool and as a QC method for the characterization of submicron systems.
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1.1 This guide deals with the measurement of particle size distribution of suspended particles, from ~10 nm to the onset of sedimentation, sample dependent, using the nanoparticle tracking analysis (NTA) 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.

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1.1 This guide deals with the measurement of mobility and zeta potential in systems containing biological material such as proteins, DNA, liposomes and other similar organic materials that possess particle sizes in the nanometer scale (  
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.

SIGNIFICANCE AND USE
5.1 Mean particle diameters defined according to the Moment-Ratio (M-R) system are derived from ratios between two moments of a particle size distribution.
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1.1 The purpose of this practice is to present procedures for calculating mean sizes and standard deviations of size distributions given as histogram data (see Practice E1617). The particle size is assumed to be the diameter of an equivalent sphere, for example, equivalent (area/surface/volume/perimeter) diameter.  
1.2 The mean sizes/diameters are defined according to the Moment-Ratio (M-R) definition system.2,3,4  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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.

SIGNIFICANCE AND USE
5.1 Au nano-objects in various shapes (that is, rods, particles) are increasingly used for a wide variety of applications. Medical applications of AuNPs, such as targeted drug delivery, tumor detection, and treatment are becoming more common (5). AuNPs have unique optical properties related to their size and their surface can be readily functionalized. Though Au is recognized to be inert and biocompatible in its bulk form, the behavior of Au nano-objects in biological systems and the environment must be tested to ensure their inertness and safety (6). It is important to know whether prepared and stored suspensions of AuNPs contain Au in its bound state (commonly Au (0) and particle adsorbed species) or ionized state (commonly, Au (I) or Au (III)) to attribute the biological response to the appropriate species. Krug, et al., concluded that the significance of toxicity studies is considerably reduced in those cases where the material properties of the nanomaterial suspensions were not characterized prior to and during the study (7). Furthermore, the analyte mass fraction of particle bound species is used with knowledge of particle size to compute particle number concentration.
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1.1 This test method describes the use of inductively coupled plasma optical emission spectrometry (ICP-OES; also includes ICP-AES, where AES is atomic emission spectrometry) or inductively coupled plasma mass spectrometry (ICP-MS) for the determination of the mass fraction of particle bound gold (Au) in colloidal Au suspensions. Particle bound Au is defined as the mass of Au associated with the nanoparticle (NP) fraction and strongly adsorbed to the particle surface. Unbound Au is the fraction of Au in the native suspension not associated with the Au nanoparticle fraction that is, the dissolved Au existing in solution as a complex or free ion. The mass fraction of particle bound Au is determined by subtracting the mass fraction of unbound Au measured in acidified subsamples of the particle-free supernatant from the total Au mass fraction measured in acid-digested subsamples of the colloidal Au suspension. The particle-free supernatant is obtained after centrifugation of the colloidal Au suspension. This standard prescribes the use of an appropriate internal standard and calibration using either external standardization or single-point standard additions.  
1.2 Colloidal gold suspensions with AuNP diameters ranging from 1 nm to 100 nm can be determined with this method.  
1.3 The standard is not limited to particles with a uniform Au composition and may be applicable to a core-shell particle with a Au shell treatment.  
1.4 This standard is specific to Au. The method may be applicable to other elements measurable by ICP-OES or ICP-MS but is limited to nanoparticles that are not reactive in aqueous suspension.  
1.5 No detailed instructions for operating instrumentation are provided because of differences among various makes and models. Instead, the analyst shall follow the instructions provided by the manufacturer of their particular ICP-OES, ICP-MS or centrifuge instrument, especially with regard to optimization of the instrument settings.  
1.6 The values stated in SI units are to be regarded as standard. No other units of measurements are included in this standard.  
1.7 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.  
1.8 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.

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.
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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.

SIGNIFICANCE AND USE
5.1 Particle size is a key property of manufactured or engineered nanoparticles used in a wide range of applications. For purposes relevant to evaluations of safety, effectiveness, performance, quality, public health impact, or regulatory status of products, the correct measurement and uniform reporting of size and related parameters under use conditions, or during the manufacturing process, are critical to suppliers, analysts, regulators and other stakeholders.  
5.2 This test method is intended principally for the analysis of nanoparticles in aqueous suspension with dimensions between about 1 nm and 100 nm, but may be applied to diffusive colloidal particles even if their dimensions fall outside the nanoscale range (up to 1000 nm).  
5.3 For more detailed guidance on DLS measurements, including operational aspects, refer to Appendix X2 of this test method.
Note 1: The user is also referred to Guide E2490, which provides broad guidance for the application of DLS to nanomaterials. Guide E2490 is not required for the implementation of this test method.
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1.1 This test method addresses the determination of nanoparticle size (equivalent sphere hydrodynamic diameter) using batch-mode (off-line) dynamic light scattering (DLS) in aqueous suspensions and establishes general procedures that are applicable to many commercial DLS instruments. This test method specifies best practices, including sample preparation, performance verification, data analysis and interpretation, and reporting of results. The document includes additional general information for the analyst, such as recommended settings for specific media, potential interferences, and method limitations. Issues specific to the use of DLS data for regulatory submissions are addressed.  
1.2 The procedures and practices described in this test method, in principle, may be applied to any particles that exhibit Brownian motion and are kinetically stable during the course of a typical experimental time frame. In practice, this includes particles up to about 1000 nm in diameter, subject to limitations as described in the test method.  
1.3 This test method does not provide test specimen preparation procedures for all possible materials and applications, nor does it address synthesis or processing prior to sampling. The test specimen (suspension) preparation procedures should provide acceptable results for a wide range of materials and conditions. The analyst must validate the appropriateness for their particular application.  
1.4 This test method is applicable to DLS instruments that implement correlation spectroscopy. Analysts using instruments based on frequency analysis may still find useful information relevant to many aspects of the measurement process, including limits of applicability and best practices. On-line (flow-mode) DLS measurements are not treated here specifically and may have additional limitations or issues relative to batch-mode operation.  
1.5 Units—The values stated in SI units are to be regarded as standard. Where appropriate, c.g.s. units are given in addition to SI.  
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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 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.

SIGNIFICANCE AND USE
4.1 The remarkable structural, physical and chemical properties of graphene — particularly its mechanical strength, high electronic mobility, lightness, and transparency (single layer or a few layers) — have generated worldwide research and industrial production efforts aimed at developing practical applications. Various industrially scalable production methods have been developed, including bottom-up approaches that grow graphene from small molecules (with or without a substrate), and top-down methods that start with graphite and exfoliate it by mechanical, chemical or electrochemical methods to produce nanoscale product such as graphene flakes. Two common exfoliation methods are: (1) oxidation of graphite to graphene oxide (GO) followed by additional processing to form reduced graphene oxide (r-GO) (2) and, (2) liquid phase exfoliation of graphite (3). The exfoliation methods, as well as substrate-less bottom-up approaches, produce materials in the form of flakes that can be dispersed in various solvents, making them suitable for applications requiring solution processing. Although there are many commercial “graphene” materials available on the market, the quality of these products is highly variable (4). There are many challenges in assessing the physical properties of the materials. In this guide we discuss how Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS), as well as atomic force microscopy (AFM) can be used to characterize materials consisting of flakes of graphene and related materials (that is, few layer graphene (FLG), GO, r-GO). Illustrative examples are provided showing how these methods can be used to identify the type of material present and to extract important parameters including lateral flake size, average flake thickness, ratio of intensities of the D and G modes (ID/IG) in the Raman spectrum and carbon to oxygen ratio. Specifically, when encountering an “unknown” material or product purporting to be “graphene,” it is essent...
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1.1 This standard will provide guidance on the measurement approaches for assessment of lateral flake size, average flake thickness, Raman intensity ratio of the D to G bands, and carbon/oxygen ratio for graphene and related products. The techniques included here are atomic force microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Examples will be given for each type of measurement.  
1.2 This guide is intended to serve as an example for manufacturers, producers, analysts, and others with an interest in graphene and related products such as graphene oxide and reduced graphene oxide. This Standard Guide is not intended to be a comprehensive overview of all possible characterization methods.  
1.3 This guide does not include all sample preparation procedures for all possible materials and applications. The user must validate the appropriateness for their particular application.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 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.  
1.6 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.

SIGNIFICANCE AND USE
5.1 Cryo-TEM is a technique used to record high resolution images of samples that are frozen and embedded in a thin layer of vitrified, amorphous ice (2-5). Because vitrification occurs so rapidly, the resultant specimen is almost instantly frozen, yielding a very accurate representation of the specimen at the moment of freezing, without the distortions typically associated with air drying delicate wet samples. Once frozen, images of the specimen are recorded at low temperature using a specially designed electron microscope equipped with a cryo-holder capable of operating under low dose conditions in order to prevent beam induced structural damage to the specimen. The cryo-TEM technique is the consensus choice to directly observe, analyze and accurately measure liposomes suspended in aqueous solutions. Fig. 1 illustrates this by comparing an electron micrograph from an air-dried negatively stained liposomal preparation with an electron micrograph of the same solution imaged by cryo-TEM.
FIG. 1 Left—An Electron Micrograph of an Air-Dried Liposomal Preparation that has been Negatively Stained with 2 % Uranyl Acetate for Contrast; Right—An Electron Micrograph of the Same Liposomal Preparation Prepared as a Frozen Vitrified Specimen for Cryo-TEM
Note 1: Both images are shown to the same scale; scale bar is 200 nm.  
5.1.1 Fig. 1 demonstrates that liposomes may become distorted and are difficult to measure and analyze when they are air-dried, while the same liposomal preparation is clearly easier to analyze when the specimen is near-instantly preserved by vitrification.  
5.1.2 Cryo-TEM involves applying a small volume of sample to a specially prepared holey, ultra-thin or continuous carbon grid suspended in a cryo-TEM plunger over a cup of liquid ethane cooled in a container filled with liquid nitrogen (2, 3). These grids can be purchased or prepared in the laboratory using a carbon evaporator with glow discharge capabilities. Once the sample has wet the surface o...
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1.1 This practice covers procedures for vitrifying and recording images of a suspension of liposomes with a cryo-transmission electron microscope (cryo-TEM) for the purpose of evaluating their shape, size distribution and lamellarity for quality assessment. The sample is vitrified in liquid ethane onto specially prepared holey, ultra-thin, or continuous carbon TEM grids, and imaged in a cryo-holder placed in a cryo-TEM.  
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.

SIGNIFICANCE AND USE
5.1 A tiered strategy for characterization of nanoparticle properties is necessary to draw meaningful conclusions concerning dose-response relationships observed during inhalation toxicology experiments. This tiered strategy includes characterization of nanoparticles as produced (that is, measured as the bulk material sold by the supplier) and as administered (that is, measured at the point of delivery to a test subject) (Oberdorster et al. (6)).  
5.2 Test Methods B922 and C1274 and ISO 9277 and ISO 18757 exist for determination of the as produced surface area of bulk metal and metal oxide powders. During the delivery of nanoparticles in inhalation exposure chambers, the material properties may undergo change and therefore have properties that differ from the material as produced. This test method describes the determination of the as administered surface area of airborne metal oxide nanoparticles in inhalation exposure chambers for inhalation toxicology studies.
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1.1 This test method covers determination of surface area of airborne metal oxide nanoparticles in inhalation exposure chambers for inhalation toxicology studies. Surface area may be measured by gas adsorption methods using adsorbates such as nitrogen, krypton, and argon (Brunauer et al. (1),2 Anderson (2), Gregg and Sing (3)) or by ion attachment and mobility-based methods (Ku and Maynard (4)). This test method is specific to the measurement of surface area by gas adsorption by krypton gas adsorption. The test method permits the use of any modern commercial krypton adsorption instruments but strictly defines the sample collection, outgassing, and analysis procedures for metal and metal oxide nanoparticles. Use of krypton is required due to the low overall surface area of particle-laden samples and the need to accurately measure the background surface area of the filter used for sample collection. Instrument-reported values of surface area based on the multipoint Brunauer, Emmett and Teller (BET) equation (Brunauer et al. (1), Anderson (2), Gregg and Sing (3)) are used to calculate surface area of airborne nanoparticles collected on a filter.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. State all numerical values in terms of SI units unless specific instrumentation software reports surface area using alternate units.  
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.

SIGNIFICANCE AND USE
5.1 Cryo-TEM is a technique used to record high resolution images of samples that are frozen and embedded in a thin layer of vitrified, amorphous ice (2-5). Because vitrification occurs so rapidly, the resultant specimen is almost instantly frozen, yielding a very accurate representation of the specimen at the moment of freezing, without the distortions typically associated with air drying delicate wet samples. Once frozen, images of the specimen are recorded at low temperature using a specially designed electron microscope equipped with a cryo-holder capable of operating under low dose conditions in order to prevent beam induced structural damage to the specimen. The cryo-TEM technique is the consensus choice to directly observe, analyze and accurately measure liposomes suspended in aqueous solutions. Fig. 1 illustrates this by comparing an electron micrograph from an air-dried negatively stained liposomal preparation with an electron micrograph of the same solution imaged by cryo-TEM.
FIG. 1 Left—An Electron Micrograph of an Air-Dried Liposomal Preparation that has been Negatively Stained with 2 % Uranyl Acetate for Contrast; Right—An Electron Micrograph of the Same Liposomal Preparation Prepared as a Frozen Vitrified Specimen for Cryo-TEM
Note 1: Both images are shown to the same scale; scale bar is 200 nm.  
5.1.1 Fig. 1 demonstrates that liposomes may become distorted and are difficult to measure and analyze when they are air-dried, while the same sample is clearly easier to analyze when the specimen is near-instantly preserved by vitrification.  
5.1.2 Cryo-TEM involves applying a small volume of sample to a specially prepared holey, ultra-thin or continuous carbon grid suspended in cryo-TEM plunger over a cup of liquid ethane cooled in a container filled with liquid nitrogen (2, 3). These grids can be purchased or prepared in the laboratory using a carbon evaporator with glow discharge capabilities. Once the sample has wet the surface of the grid, and s...
SCOPE
1.1 This practice covers procedures for vitrifying and recording images of a suspension of liposomes with a cryo-transmission electron microscope (cryo-TEM) for the purpose of evaluating their shape, size distribution and lamellarity for quality assessment. The sample is vitrified in liquid ethane onto specially prepared holey, ultra-thin, or continuous carbon TEM grids, and imaged in a cryo-holder placed in a cryo-TEM.  
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.

SIGNIFICANCE AND USE
5.1 Cryo-TEM is a technique used to record high resolution images of samples that are frozen and embedded in a thin layer of vitrified, amorphous ice (2-5). Because vitrification occurs so rapidly, the resultant specimen is almost instantly frozen, yielding a very accurate representation of the specimen at the moment of freezing, without the distortions typically associated with air drying delicate wet samples. Once frozen, images of the specimen are recorded at low temperature using a specially designed electron microscope equipped with a cryo-holder capable of operating under low dose conditions in order to prevent beam induced structural damage to the specimen. The cryo-TEM technique is the consensus choice to directly observe, analyze and accurately measure liposomes suspended in aqueous solutions. Fig. 1 illustrates this by comparing an electron micrograph from an air-dried negatively stained liposomal preparation with an electron micrograph of the same solution imaged by cryo-TEM.
FIG. 1 Left—An Electron Micrograph of an Air-Dried Liposomal Preparation that has been Negatively Stained with 2 % Uranyl Acetate for Contrast; Right—An Electron Micrograph of the Same Liposomal Preparation Prepared as a Frozen Vitrified Specimen for Cryo-TEM
Note 1: Both images are shown to the same scale; scale bar is 200 nm.  
5.1.1 Fig. 1 demonstrates that liposomes may become distorted and are difficult to measure and analyze when they are air-dried, while the same sample is clearly easier to analyze when the specimen is near-instantly preserved by vitrification.  
5.1.2 Cryo-TEM involves applying a small volume of sample to a specially prepared holey, ultra-thin or continuous carbon grid suspended in cryo-TEM plunger over a cup of liquid ethane cooled in a container filled with liquid nitrogen (2, 3). These grids can be purchased or prepared in the laboratory using a carbon evaporator with glow discharge capabilities. Once the sample has wet the surface of the grid, and s...
SCOPE
1.1 This practice covers procedures for vitrifying and recording images of a suspension of liposomes with a cryo-transmission electron microscope (cryo-TEM) for the purpose of evaluating their shape, size distribution and lamellarity for quality assessment. The sample is vitrified in liquid ethane onto specially prepared holey, ultra-thin, or continuous carbon TEM grids, and imaged in a cryo-holder placed in a cryo-TEM.  
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.

SCOPE
1.1 This guide deals with the measurement of mobility and zeta potential in systems containing biological material such as proteins, DNA, liposomes and other similar organic materials that possess particle sizes in the nanometer scale (  
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.

SIGNIFICANCE AND USE
5.1 Mean particle diameters defined according to the Moment-Ratio (M-R) system are derived from ratios between two moments of a particle size distribution.
SCOPE
1.1 The purpose of this practice is to present procedures for calculating mean sizes and standard deviations of size distributions given as histogram data (see Practice E1617). The particle size is assumed to be the diameter of an equivalent sphere, for example, equivalent (area/surface/volume/perimeter) diameter.  
1.2 The mean sizes/diameters are defined according to the Moment-Ratio (M-R) definition system.2,3,4  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 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.  
1.5 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.

SIGNIFICANCE AND USE
5.1 NTA 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 describes the NTA technique for direct visualization and measurement of Brownian motion, generally applicable in the particle size range from several nanometers until the onset of sedimentation in the sample. The NTA technique is usually applied to dilute 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 size diameters determined by other techniques and users of the NTA technique need to be aware of the distinction of the various descriptors of particle diameter before making comparisons between techniques (see 8.7). Notwithstanding the preceding sentence, the technique is routinely 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, from ~10 nm to the onset of sedimentation, sample dependent, using the nanoparticle tracking analysis (NTA) 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.

SIGNIFICANCE AND USE
5.1 As AFM measurement technology has matured and proliferated, the technique has been widely adopted by the nanotechnology research and development community to the extent that it is now considered an indispensible tool for visualizing and quantifying structures on the nanoscale. Whether used as a stand-alone method or to complement other dimensional measurement methods, AFM is now a firmly established component of the nanoparticle measurement tool box. International standards for AFM-based determination of nanoparticle size are nonexistent as of the drafting of this guide. Therefore, this standard aims to provide practical and metrological guidance for the application of AFM to measure the size of substrate-supported nanoparticles based on maximum displacement as the probe is rastered across the particle surface to create a line profile.
SCOPE
1.1 The purpose of this document is to provide guidance on the quantitative application of atomic force microscopy (AFM) to determine the size of nanoparticles2 deposited in dry form on flat substrates using height (z-displacement) measurement. Unlike electron microscopy, which provides a two-dimensional projection or a two-dimensional image of a sample, AFM provides a three-dimensional surface profile. While the lateral dimensions are influenced by the shape of the probe, displacement measurements can provide the height of nanoparticles with a high degree of accuracy and precision. If the particles are assumed to be spherical, the height measurement corresponds to the diameter of the particle. In this guide, procedures are described for dispersing gold nanoparticles on various surfaces such that they are suitable for imaging and height measurement via intermittent contact mode AFM. Generic procedures for AFM calibration and operation to make such measurements are then discussed. Finally, procedures for data analysis and reporting are addressed. The nanoparticles used to exemplify these procedures are National Institute of Standards and Technology (NIST) reference materials containing citrate-stabilized negatively charged gold nanoparticles in an aqueous solution.  
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 and health 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.

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 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 and health practices and determine the applicability of regulatory limitations prior to use.

SIGNIFICANCE AND USE
5.1 A tiered strategy for characterization of nanoparticle properties is necessary to draw meaningful conclusions concerning dose-response relationships observed during inhalation toxicology experiments. This tiered strategy includes characterization of nanoparticles as produced (that is, measured as the bulk material sold by the supplier) and as administered (that is, measured at the point of delivery to a test subject) (Oberdorster et al., 2005) (6).  
5.2 Test Methods B922 and C1274 and ISO Standards 9277 and 18757 exist for determination of the as produced surface area of bulk metal and metal oxide powders. During the delivery of metal and metal oxide nanoparticles in inhalation exposure chambers, the material properties may undergo change and therefore have properties that differ from the material as produced. This test method describes the determination of the as administered surface area of airborne metal and metal oxide nanoparticles in inhalation exposure chambers for inhalation toxicology studies.
SCOPE
1.1 This test method covers determination of surface area of airborne metal and metal oxide nanoparticles in inhalation exposure chambers for inhalation toxicology studies. Surface area may be measured by gas adsorption methods using adsorbates such as nitrogen, krypton, and argon (Brunauer et al., 1938; Anderson, 1975; Gregg and Sing, 1982) (1, 2, 3)2 or by ion attachment and mobility-based methods (Ku and Maynard, 2005) (4). This test method is specific to the measurement of surface area by gas adsorption by krypton gas adsorption. The test method permits the use of any modern commercial krypton adsorption instruments but strictly defines the sample collection, outgassing, and analysis procedures for metal and metal oxide nanoparticles. Use of krypton is required due to the low overall surface area of particle-laden samples and the need to accurately measure the background surface area of the filter used for sample collection. Instrument-reported values of surface area based on the multipoint Brunauer, Emmett and Teller (BET) equation (Brunauer et al., 1938; Anderson, 1975; Gregg and Sing, 1982) (1, 2, 3) are used to calculate surface area of airborne nanoparticles collected on a filter.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. State all numerical values in terms of SI units unless specific instrumentation software reports surface area using alternate units.  
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 and health practices and determine the applicability of regulatory limitations prior to use.

SIGNIFICANCE AND USE
Mean particle diameters defined according to the Moment-Ratio (M-R) system are derived from ratios between two moments of a particle size distribution.
SCOPE
1.1 The purpose of this practice is to present procedures for calculating mean sizes and standard deviations of size distributions given as histogram data (see Practice E1617). The particle size is assumed to be the diameter of an equivalent sphere, for example, equivalent (area/surface/volume/perimeter) diameter.
1.2 The mean sizes/diameters are defined according to the Moment-Ratio (M-R) definition system. , ,  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.

SIGNIFICANCE AND USE
NTA 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 describes the NTA technique for direct visualization and measurement of Brownian motion, generally applicable in the particle size range from several nanometers until the onset of sedimentation in the sample. The NTA technique is usually applied to dilute 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 size diameters determined by other techniques and users of the NTA technique need to be aware of the distinction of the various descriptors of particle diameter before making comparisons between techniques (see 8.7). Notwithstanding the preceding sentence, the technique is routinely 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, from ~10 nm to the onset of sedimentation, sample dependent, using the nanoparticle tracking analysis (NTA) 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 and health practices and determine the applicability of regulatory limitations prior to use.

SCOPE
1.1 This guide deals with the measurement of mobility and zeta potential in systems containing biological material such as proteins, DNA, liposomes and other similar organic materials that possess particle sizes in the nanometer scale (100 nm).
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 and health practices and determine the applicability of regulatory limitations prior to use.

SIGNIFICANCE AND USE
As AFM measurement technology has matured and proliferated, the technique has been widely adopted by the nanotechnology research and development community to the extent that it is now considered an indispensible tool for visualizing and quantifying structures on the nanoscale. Whether used as a stand-alone method or to complement other dimensional measurement methods, AFM is now a firmly established component of the nanoparticle measurement tool box. International standards for AFM-based determination of nanoparticle size are nonexistent as of the drafting of this guide. Therefore, this standard aims to provide practical and metrological guidance for the application of AFM to measure the size of substrate-supported nanoparticles based on maximum displacement as the probe is rastered across the particle surface to create a line profile.
SCOPE
1.1 The purpose of this document is to provide guidance on the quantitative application of atomic force microscopy (AFM) to determine the size of nanoparticles deposited in dry form on flat substrates using height (z-displacement) measurement. Unlike electron microscopy, which provides a two-dimensional projection or a two-dimensional image of a sample, AFM provides a three-dimensional surface profile. While the lateral dimensions are influenced by the shape of the probe, displacement measurements can provide the height of nanoparticles with a high degree of accuracy and precision. If the particles are assumed to be spherical, the height measurement corresponds to the diameter of the particle. In this guide, procedures are described for dispersing gold nanoparticles on various surfaces such that they are suitable for imaging and height measurement via intermittent contact mode AFM. Generic procedures for AFM calibration and operation to make such measurements are then discussed. Finally, procedures for data analysis and reporting are addressed. The nanoparticles used to exemplify these procedures are National Institute of Standards and Technology (NIST) reference materials containing citrate-stabilized negatively charged gold nanoparticles in an aqueous solution.
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 and health practices and determine the applicability of regulatory limitations prior to use.

SIGNIFICANCE AND USE
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 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 and health practices and determine the applicability of regulatory limitations prior to use.

SIGNIFICANCE AND USE
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 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 and health practices and determine the applicability of regulatory limitations prior to use.

SCOPE
1.1 The purpose of this practice is to present procedures for calculating mean sizes and standard deviations of size distributions given as histogram data (see Practice E 1617). The particle size is assumed to be the diameter of an equivalent sphere, e.g., equivalent (area/surface/volume/perimeter) diameter.
1.2 The mean sizes/diameters are defined according to the Moment-Ratio (M-R) definition system.
1.3 This practice uses SI (Systeme International) units as standard.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.