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ISO/TS 28037:2010 — Nanotechnologies — Guidance on measurement methodology for particle size distribution and shape
ISO/TS 28037:2010 | Nanomaterial Measurement Guidance Standard
Introduction to ISO/TS 28037:2010
ISO/TS 28037:2010, “Nanotechnologies — Guidance on measurement methodology for particle size distribution and shape,” provides a comprehensive framework for selecting, executing, and validating measurement techniques for nanomaterials. Unlike ISO/TS 27687 which focuses on definitions, this Technical Specification addresses the practical challenges of obtaining reliable, reproducible measurements of nanomaterial characteristics — a task that is notoriously difficult due to the small size scales, high surface reactivity, and strong agglomeration tendencies of nano-objects. Developed by ISO/TC 229, the standard fills a critical gap between the theoretical understanding of nanomaterial properties and the practical reality of measuring them with confidence.
When developing a quality control protocol for nanomaterial production, ISO/TS 28037:2010 is the essential companion to ISO/TS 27687. The definitions tell you what to call it; this specification tells you how to measure it. Together they form the basis for any defensible nanomaterial characterization strategy.
The standard covers measurement of particle size distribution (PSD), mean particle size, specific surface area (SSA), and particle shape descriptors. It provides guidance on the selection of appropriate measurement techniques based on the material type, the expected size range, the sample preparation methodology, and the required measurement uncertainty. Critically, the specification emphasizes that no single measurement technique is universally applicable — each method has inherent biases that must be understood and accounted for when interpreting results. The choice of technique should be guided by the specific question being asked: are you measuring primary particle size for material classification, hydrodynamic size for biocompatibility assessment, or agglomerate size for quality control during manufacturing?
The specification also addresses the important topic of measurement traceability, recommending that all measurements be traceable to SI units through an unbroken chain of calibrations. For nanoscale measurements, this typically means calibrating instruments with certified reference materials (CRMs) of known particle size, such as colloidal gold nanoparticles or polystyrene latex spheres. The standard provides guidance on selecting appropriate CRMs, establishing calibration protocols, and estimating the uncertainty contribution from the calibration chain.
Measurement Techniques and Their Applicability
The specification surveys the major measurement techniques available for nanomaterial characterization and provides a detailed comparison matrix to guide method selection. The key insight is that different measurement principles probe different physical properties and thus can produce different results for the same sample. For example, dynamic light scattering (DLS) measures the hydrodynamic diameter — which includes the solvation layer and any adsorbed species — while transmission electron microscopy (TEM) measures the physical core diameter in a dry, high-vacuum environment. Both are valid measurements of “particle size,” but they answer different questions and will not necessarily agree. Understanding these differences is essential for both method selection and data interpretation.
| Technique | Measured Property | Size Range | Strengths | Limitations |
|---|---|---|---|---|
| Transmission Electron Microscopy (TEM) | Physical core diameter, morphology, crystallinity | 1 nm – 5 um | Direct visualization, shape information, elemental analysis (EDS) | Small sampling volume (typically <1000 particles), vacuum required, possible drying artifacts |
| Scanning Electron Microscopy (SEM) | Surface morphology, agglomerate structure, topography | 10 nm – 1 mm | 3D-like imaging, larger field of view, minimal sample preparation | Lower resolution than TEM, conductive coating needed for non-conductive samples |
| Dynamic Light Scattering (DLS) | Hydrodynamic diameter, polydispersity index (PDI) | 1 nm – 6 um | Fast measurement (<5 min), high statistical precision, in-suspension native state | Biased toward larger particles, assumes spherical shape, sensitive to dust and aggregates |
| Atomic Force Microscopy (AFM) | Height (z-dimension), 3D topography, agglomerate morphology | 1 nm – 10 um | Sub-nanometer z-resolution, works in air or liquid, no special sample coating | Tip convolution artifacts, slow scan speed, limited field of view |
| Nitrogen Adsorption (BET) | Specific surface area, porosity | SSA 0.01 – 2000 m2/g | Well-established standard (ISO 9277), large sampling volume, industry standard | No direct PSD, requires dry powder, assumes uniform surface properties |
| Small-Angle X-ray Scattering (SAXS) | Electron density correlation distance, size, shape | 1 nm – 100 nm | Ensemble average over large sample volume, in situ capability, no drying needed | Complex data interpretation requiring modeling, limited access to synchrotron sources |
| Nanoparticle Tracking Analysis (NTA) | Number-based PSD, particle concentration | 10 nm – 2 um | Number-weighted distribution, particle-by-particle counting with video | Requires careful optimization of camera gain, focus, and analysis settings |
Reporting particle size without specifying the measurement technique and the metric (e.g., Z-average from DLS vs. number-weighted mode from TEM) is a common cause of confusion and controversy in nanotechnology literature. Always state both the method and the metric. A difference of 50% or more between different techniques for the same sample is not unusual and does not necessarily indicate measurement error.
Sample Preparation and Data Reporting
ISO/TS 28037:2010 dedicates significant attention to sample preparation, recognizing that the way a nanomaterial is dispersed, diluted, and deposited strongly influences measurement outcomes. The specification provides detailed protocols for dispersion in liquids (using controlled sonication, appropriate surfactants, and pH adjustment), deposition on substrates (electrostatic capture, drop-casting, spin-coating), and preparation for electron microscopy (cryo-fixation, staining, and sectioning). It emphasizes the importance of reporting dispersion protocols in sufficient detail to enable reproducibility — a practice that is regrettably uncommon in much of the published nanotechnology literature. The standard recommends recording sonication energy input (not just time), final pH and conductivity of dispersions, and the time between preparation and measurement.
The data reporting framework requires that measurement results include not only the central tendency (mean, median, mode) but also the distribution width (standard deviation, interquartile range), the number of particles or measurements included, the confidence interval for the reported values, and a statement of measurement uncertainty traceable to reference standards. For PSD reporting, the specification recommends presenting both number-weighted and volume-weighted distributions whenever possible, as these emphasize different aspects of the population. A number-weighted distribution is most relevant for toxicological assessment, while a volume-weighted distribution is more relevant for understanding material properties and process behavior.
Laboratories that adopt the measurement reporting guidelines from ISO/TS 28037:2010 report significantly improved inter-laboratory reproducibility in nanomaterial characterization, often reducing between-lab variability by 40-60% compared to non-standardized protocols. This has been demonstrated in several round-robin studies organized by OECD and ISO.
The most frequently encountered quality issue in nanomaterial measurement is insufficient sample statistics. Many published studies report particle size distributions based on fewer than 100 particles from TEM images, yielding confidence intervals that span an order of magnitude. The specification recommends a minimum of 300-500 particles for statistically meaningful PSD reporting, and even more for samples with high polydispersity.
Frequently Asked Questions
Q1: Which measurement technique should I choose for routine quality control?
A: For routine QC, DLS is often preferred due to its speed, low cost, and ease of use. However, it should be validated against an orthogonal method (e.g., TEM or NTA) during method development. The standard provides a decision tree that considers material type, expected size range, and measurement purpose.
A: For routine QC, DLS is often preferred due to its speed, low cost, and ease of use. However, it should be validated against an orthogonal method (e.g., TEM or NTA) during method development. The standard provides a decision tree that considers material type, expected size range, and measurement purpose.
Q2: How should I handle agglomerated samples?
A: The specification distinguishes between primary particle size and agglomerate size. Both should be reported, and the dispersion protocol used should be described in detail. In situ measurements (e.g., DLS in the native suspension medium) are preferred over measurements requiring drying, as drying can induce additional agglomeration artifacts.
A: The specification distinguishes between primary particle size and agglomerate size. Both should be reported, and the dispersion protocol used should be described in detail. In situ measurements (e.g., DLS in the native suspension medium) are preferred over measurements requiring drying, as drying can induce additional agglomeration artifacts.
Q3: Can ISO/TS 28037:2010 be used for regulatory submissions?
A: Yes. Regulatory bodies including the European Chemicals Agency (ECHA) and the US Environmental Protection Agency (EPA) accept measurement data generated in accordance with this specification as part of nanomaterial registration dossiers. Compliance with the standard demonstrates that appropriate attention has been given to method selection and data quality.
A: Yes. Regulatory bodies including the European Chemicals Agency (ECHA) and the US Environmental Protection Agency (EPA) accept measurement data generated in accordance with this specification as part of nanomaterial registration dossiers. Compliance with the standard demonstrates that appropriate attention has been given to method selection and data quality.
Q4: How do I determine measurement uncertainty for PSD?
A: The standard recommends following the ISO/IEC Guide 98 (GUM) framework for uncertainty estimation. Key contributors include sample preparation variability, instrument calibration uncertainty, operator effects, and statistical sampling uncertainty. For TEM-based measurements, the statistical contribution from limited particle counting often dominates the total uncertainty budget.
A: The standard recommends following the ISO/IEC Guide 98 (GUM) framework for uncertainty estimation. Key contributors include sample preparation variability, instrument calibration uncertainty, operator effects, and statistical sampling uncertainty. For TEM-based measurements, the statistical contribution from limited particle counting often dominates the total uncertainty budget.
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