I have calculated Z-average particle size from Dynamic Light Scattering (Zeta sizer). But, almost all the literature I am willing to cite for comparison has been reported diameter by volume-based diameters such as d(3,2) or d(4,3).
How should I compare and report in my article?
Will it be justified to report number-based diameter (my result) and volume-based (literature) together?
You can't. If you only have z-average diameters, it is impossible to calculate a corresponding d(3,2) or d(4,3), or any other value that requires knowledge of the distribution. z-average is a single value. That value could be obtained from an infinite number of distributions.
You should only report what the instrument can realistically tell you. Note, the z-average is intensity-weighted due to the way the technique works. Just report it and state the exact instrument and settings used (especially the scattering angle). Also report the polydispersity index.
If you have access to the full Zetasizer report files, you should be able to get an estimate of the distribution, assuming the optical properties are correct. That's also true of laser diffraction results (which I suspect the d(4,3) etc are).
For many real-world materials, especially crystalline materials with multiple refractive indexes, it's hard to give the right optical parameters. This means there will be significant uncertainty in the calculated distributions. Stick with the z-average but be clear to state that's what it is.
Ayushi Kapoor This question and similar has been asked and answered on RG many times and a search on this forum will be productive. d(3,2) or d(4,3) are weighted surface and volume diameters usually obtained from laser diffraction (LD) rather than DLS. LD generally provides more resolution than DLS because of examination of multiple angular information. The most robust parameters in DLS are the z-average and PDI. With perfect data and optical properties then one can transform the intensity distribution to volume. However, this is not advised for broad distributions. The narrower the distribution then the more valid the transformation will be. Look for posts by Ulf Nobbmann on RG and also on MaterialsTalks. For example: https://www.materials-talks.com/intensity-volume-number-which-size-is-correct/
The international standards (ISO and ASTM) tell you to never convert the intensity distribution to number.
Alan F Rawle Thank you for answering the question.
Yes, I have been through other answers, especially your answers on this topic. But my specific question is, will it be fair to compare my results (in Z-average) with the existing literature (d4,3 and d3,2) ?
My question is not about 'conversion' but about 'comparison'.
Ayushi Kapoor
No. You are comparing apples with turnips (not even apples with pears) - they may both be food but they're not the same. It's important to note why these are different ways of expressing the mean value of a distribution. This is really a math issue rather than a particle size analysis one. The values will only be identical for a perfectly monodisperse distribution. They may be closer depending on the width of the distribution.
Alan F Rawle So should I look for literature reporting Z-average to compare my results?
Ayushi Kapoor Tell us more about your system and why you used DLS rather than another light scattering technique. What other techniques did you you use to gain particle size information? What is the reason for the measurement of size (distribution)?
Ayushi Kapoor "My question is not about 'conversion' but about 'comparison'."
Did you read my answer? I'll repeat the key bit:
If you only have z-average diameters, it is impossible to calculate a corresponding d(3,2) or d(4,3), or any other value that requires knowledge of the distribution. z-average is a single value. That value could be obtained from an infinite number of distributions.
So, how can you compare? You can't. Unless the d(4,3) and d(3,2) are very similar, indicating a narrow distribution, and your DLS PDI values are small, too.
Ayushi Kapoor "So should I look for literature reporting Z-average to compare my results?"
Just report your z-average and be clear that it is the z-average. You may want to include previously published d(4,3) etc but explain that comparison is not readily possible. Let the reader make the mistake of comparing if they want to. You just need to add the disclaimer.
Ayushi Kapoor
There is a dichotomy in your question ('How to compare and report Z-average diameter and volume-based diameter of particle size?') and your last sentence) in the following text (Will it be justified to report number-based diameter (my result) and volume-based (literature) together?). The Zetasizer does not measure number-based results - the z-average is a harmonically weighted intensity mean - an ensemble, not single particle, result. We need to know more about your system especially in terms of size distribution. Use of D[4.3]'s implies micron-plus sized material. Just what is the mean size of your system? Can you attach any .dts results as this will allow more specific, rather than general, comments to be made?
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