In 2019, two national metrology institutes \u2014 Japan\u2019s NMIJ and the United States\u2019 NIST \u2014 ran what should have been the least surprising experiment in materials science. Both received particles from the same manufactured lot: polystyrene spheres, certified at 30, 50, 70 and 100 nanometres, about as well-behaved as particles get. Both used dynamic light scattering (DLS), a standard sizing technique. These are the laboratories other laboratories calibrate against. And as the study published in Metrologia<\/em> reports, the apparent particle sizes were \u201cinvariably observed to disagree with each other.\u201d<\/p>\n The uncomfortable finding was that both institutes were right. The instruments differed in laser wavelength, scattering angle, and sample concentration \u2014 and each of those quietly changes the number a DLS instrument reports. Only after the physicists corrected for every parameter did the two labs converge. Even then, the technique read the certified 29 nm particles as 33.2 nm \u2014 roughly 14% large \u2014 because DLS doesn\u2019t measure the particle itself. It measures the particle plus<\/em> the shell of water moving with it. The paper notes that international comparisons have generally found \u201ca conspicuous difference\u201d between DLS and methods that measure geometry directly, such as electron microscopy.<\/p>\n The stakes get clearer in a case documented by the EU and US nanomedicine characterisation laboratories. A sample measured by DLS showed a main peak at 87 nm \u2014 a tidy result. Laser diffraction on the same material found something else: a second population at 7.7 micrometres, nearly a hundred times larger, which DLS had missed entirely because large particles settle out of the laser\u2019s path. One instrument said \u201cuniform nano-suspension.\u201d The other said \u201ccontains visible-scale aggregates.\u201d Same sample.<\/p>\n Those two laboratories \u2014 the European Nanomedicine Characterisation Lab and the US National Cancer Institute\u2019s characterisation lab, which screen materials before they reach regulators \u2014 drew a formal conclusion: \u201cno single technique is capable to measure the particle size distribution\u201d of every sample under every condition. Their standard practice is orthogonal measurement: multiple independent methods, cross-checked, with electron microscopy as the only direct witness to what crystals actually look like.<\/p>\n Hydroxyapatite buyers live downstream of this physics. A \u201cD50 of 5 \u00b5m\u201d is not a property of the powder alone \u2014 it is a property of the powder plus the instrument, its settings, and the dispersion state of the sample. So the questions that matter on a datasheet are the ones metrologists ask each other: Which method produced this number? Dispersed or as-supplied? What are the D10 and D90, not just the median? Are there electron microscope images of this<\/em> grade?<\/p>\n If national laboratories need corrections to agree with each other, no buyer should compare two suppliers\u2019 numbers at face value. What can be compared is consistency: whether a supplier\u2019s distribution holds from lot to lot on the same declared method. That is a discipline of process control \u2014 the reason tightly controlled grades, such as Japanese eggshell-derived hydroxyapatite, are specified not for the figure on the sheet but because every delivery measures the same.<\/p>\n Sources: Takahashi et al. 2019, Metrologia (open access via PMC)<\/a>; Caputo et al. 2019, Journal of Controlled Release (open access)<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":" Japan\u2019s NMIJ and America\u2019s NIST measured the same bottle of reference particles with gold-standard instruments. The numbers disagreed. So what does the particle size on your supplier\u2019s datasheet really mean?<\/p>\n","protected":false},"author":1,"featured_media":221,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_yoast_wpseo_meta-robots-noindex":"","_yoast_wpseo_meta-robots-nofollow":"","_yoast_wpseo_bctitle":"","_yoast_wpseo_canonical":"","_yoast_wpseo_opengraph-title":"","_yoast_wpseo_opengraph-description":"","_yoast_wpseo_opengraph-image":"","_yoast_wpseo_opengraph-image-id":0,"_yoast_wpseo_twitter-title":"","_yoast_wpseo_twitter-description":"","_yoast_wpseo_twitter-image":"","_yoast_wpseo_twitter-image-id":0,"footnotes":""},"categories":[4],"tags":[52,51,41,21,46],"class_list":["post-220","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research-science","tag-laser-diffraction","tag-particle-size","tag-procurement","tag-quality-control","tag-specification"],"yoast_head":"\nNothing Was Broken<\/h2>\n
The Population One Instrument Couldn\u2019t See<\/h2>\n
What the Gatekeepers Concluded<\/h2>\n
What This Means at the Purchasing Desk<\/h2>\n
The Number That Actually Predicts Performance<\/h2>\n