In my opinion, a priori it would not be possible to differentiate whether this variation is due to the nature of the sample, the uncertainty of the measuring instrument, its drift or the uncertainty due to intermediate precision (vim). Some of these parameters can be in the calibration certificate, but others can only be determined by a correct validation of the process. Analysis of these variances will indicate the probable origin of these variations.

Dear Arusha Acharyya

These links might be an asset, have a look:

1. https://www.researchgate.net/post/I-am-getting-different-results-from-DLS-measurements-what-kind-of-errors-I-might-have-or-what-can-be-the-reason

2. https://www.horiba.com/en_en/dynamic-light-scattering-dls-particle-size-distribution-analysis/

3. https://www.materials-talks.com/blog/2017/07/11/dls-in-30-minutes-qa/

Kind Regards

Qamar Ul Islam

Hello Arusha Acharyya

DLS typically should have a repeatability of 5% or better. If the two measurement conditions are the same (same temperature, concentration, buffer, cuvette, parameters in the software etc.) then 90nm is significantly different from 80nm. So check what else besides time might be different to rule that out. It might also be instructive to look at the particle size distribution, to see if only a few larger particles appear over time, or oligomers (re-)appear (e.g. after filtration).

You might find this post for "the best DLS to expect" of interest https://www.materials-talks.com/blog/2018/05/31/polydispersity-from-a-gold-standard/