I currently did my particle size analysis using Anton Paar Litesizer. I got different results when did with Omega cuvette and Disposable cuvette. The only difference I see is the path length, so does changing the concentration fix the problem?? Or is there anything else that I need to know.
Hello,
High concentration of your sample can be the reasons of DLS result difference. In case your sample is too concentrated for the DLS measurements (method considers your particles as a Brownian, meaning not interacting ones), different effects can be present: multiparticle scattering, absorption of the scattered light by your suspension as well as attraction or repulsion between the particles by themself. All of them affects the results of DLS measurements and shifts the obtained results compared to the real size of your particles. The absorption of scattered light and multiparticle scattering can be vanished in case of decreasing of optical path of the light ( please check as an example https://www.cordouan-tech.com/wp-content/uploads/2022/05/NA02-VASCO-Ink-measurement-by-DLS-with-VASCO-Analyzer_EN.pdf) or by dilution. While, the attraction/repulsion can be vanished only by diluting of the sample.
I am not sure where in the omega cuvette is focalized the beam and if it is possible that the multiparticle scattering or absorption can be vanished by using omega cuvette, so I will also advise you to consider the possibility that your suspension is not homogenous (meaning there are big objects present in very small amount, such as aggregates or dust). In this case it is possible that their presence will affects on your results obtained by cumulants method (and consequently on z average). To remove these big inhomoginities the centrifugation and/or filtration can be used.
Hi Tejashwini,
Cuvettes used for zeta potential measurement are usually working only at selected angles (the forward detector for zeta, forward and backscatter detectors for the size). I would check at which detection angle your instrument is set. AP Litesizer should have an automatic setting function which choose the best angle for the measurement
If you have a standard (polystyrene spheres for example), I would test it in the two different cuvette, to exclude a sample-related non-conformity
I would also consider in general the sample preparation protocol (how are you adding your sample to the two different cuvettes?) and how different are the results (is there a significative stepchange? what is the PI? how broad is your size distribution peak, etc.)
I hope this can be of any help!
Hi Tejashwini Lnu
are both measurements done at the same scattering angle? It is possible that the data in your disposable were at 90 and the ones in the zeta cuvette at backscattering. There are a few reasons why they then could be different, see https://www.materials-talks.com/how-do-dls-size-results-differ-with-angle/
In addition, multiple scattering, particle-particle interactions, or sample changes (due to the applied field, i.e. not exactly the same sample in both measurements) may play a role in your situation.
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