Back to Basics of Laser Diffraction – Q&A from Masterclass Part 3
Welcome to the final installment of our blog series answering questions from the back-to-basics of laser diffraction webinar. If you missed the first two blog posts, please find them here. In this blog series, we are addressing some of the excellent questions raised during the back-to-basics webinar, expanding on the topics covered to bring greater clarity.
Innovating with Adaptive Diffraction
Adaptive diffraction is a brand-new way to process your laser diffraction data that garnered significant interest during our webinar series. This section addresses your questions about adaptive diffraction and size sure.
Q – In order to use adaptive diffraction should we erase non-compliance results. Could you elaborate a little bit more size sure?
A – When using Size Sure you never lose or delete data. You can ‘Extract a classic result’ when taking a measurement with adaptive diffraction which will generate a record as if Size Sure had not been used. Size Sure can be used to help troubleshoot unexpected peaks in particle size distributions as the classification algorithm will inform the user whether the scattering is transient throughout the measurement or is frequently occurring, i.e., part of the steady state. It is then up to the user to determine whether transient signals could be reduced or removed by improved methods (e.g., bubbles could be minimized by degassing the dispersant, contaminants could be removed by improved cleaning procedures).
Q – We have an earlier model Mastersizer 3000, which has the red and blue lasers and the enhanced pharma software. Can this instrument be upgraded with the AI software?
A – We are currently exploring our options based on similar feedback from other customers. Keep an eye on our website for any future updates.
Q – For the MS3000, one way we have to control these transition states was by enabling the option to keep a single result. In some cases, we suggest that it has worked because out of approximately 50 measurements, 1 had this bimodal profile. Can we suggest that it is a way to mitigate this effect?
A – Yes, Keep a Single Result Mode (KSRM) is a valid way of removing phantom peaks from a particle size distribution (PSD). However, before excluding data from the PSD it is important to verify whether the peak could have come from the particles in the sample. Visual inspections of the sample for very large material or using an orthogonal technique such as microscopy can help. Additionally, understanding the sample’s processing is useful. For instance, if the sample was passed through a 250 µm sieve and there is a mode >1000 µm, it is unlikely related to the sample.
When using KSRM we advise running the measurement without it enabled in the SOP. Then if you see an additional peak, investigate it as recommended above. If you are confident that the peak it is not related to your sample, then you can apply KSRM to remove it during post-processing.
Decoding data – particle size distributions
Finally, we focus on size distributions, a critical aspect of particle size analysis. Your questions about interpreting and utilizing size distribution data were excellent. Let’s discuss what we measure on the Mastersizer together and understand its implications.
Q – Can the software provide number distribution of particles as opposed to volume distribution? Also, can it provide absolute number of particles measured for different diameter (as opposed to %)?
Q – What is exactly the y-axis “volume density” indicating? there is an option that is number density. Does it mean we are also able to quantify the number of particles when measuring the size?
A – Laser diffraction results, such as those from the Mastersizer 3000(+), report a volume weighted particle size distribution. The default y-axis, ‘Volume Density (%)’, shows the percentage of the total sample volume in each size class. While you can convert volume-based results to a number distribution, this mathematical process may amplify any errors in the original data. Therefore, we advise caution when using the number distribution to quantify the absolute number of particles, as laser diffraction is not a particle counting technique. To convert to a number or surface area distribution, edit the result and select the ‘Result type’ in the settings.
Q – Could you also convert to a mass distribution, if the density of the particles is all the same?
A – Yes, if you know the density is uniform across the size range you can assume equivalence between a volume and mass distribution.
Q – What the intensity of the particle size distribution can tell about the proportions of particle sizes?
A – For laser diffraction measurements the distribution we report is a volume weighted distribution. When using Dynamic Light Scattering (DLS) to measure particle size using the Zetasizer Advance range you will get an intensity weighted size distribution.
Q – If I understand correctly than the size distribution is mathematically generated from the batch measurements. How big is the difference in size your algorithm can resolve?
A – For a classic laser diffraction measurement, the result is computed from scattering data that is collected at 10kHz throughout the duration of the measurement. This scattering is then averaged and a particle size distribution is computed from the average scattering data using the chosen optical model (e.g., Mie or Fraunhofer). There is now also the option to use Adaptive Diffraction when measuring with your Mastersizer 3000+ which classifies the data into steady and transient states and produces a PSD for each classification, giving you greater clarity and improved confidence in your results.
The Mastersizer 3000 and 3000+ instruments have been tested to show excellent accuracy, repeatability and reproducibility using NIST traceable standards. Depending on the instrument model you have (Lab, Pro, Ultra) and dispersion accessory the dynamic range of the instrument can span from 0.01 to 3500 um giving it a very wide dynamic range and sensitivity across a range of size classes.
Further resources and webinar recordings
Thank you again for your engagement throughout the Mastersizer Masterclass. If you would like to revisit the webinars please find the recordings on our website. For more information on laser diffraction applications and method development, please visit our knowledge center where you can find a library of application notes, technical notes and blog posts on a range of topics. And if you would like to ask more specific questions, please do get in touch via our customer support portal where your enquiry will be passed on to the relevant technical expert. Stay tuned for the final blog in the series where we cover adaptive diffraction and understanding size distributions.
Further reading
- Back to Basics of Laser Diffraction – Q&A from Masterclass Part 3
- Back to Basics of Laser Diffraction – Q&A from Masterclass Part 2
- Back to Basics of Laser Diffraction – Q&A from Masterclass Part 1
- Precision on the Loch: delivering Mastersizer 3000+ training on the Isle of Skye and exploring its scientific wonders
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