Hello, I am having issues to the Zetasizer Nano ZS that I was hoping someone could give me some ideas to try and fix please.
I am attempting to run critical micelle concentration analysis with the dispersant of water.
However, my water blank will not pass the quality criteria.
I have filtered it through a 0.2um filter, i have tried double filterring as well as using HPLC grade water and filtered HPLC grade water.
When running the machine sizing standard through the system it states it has passed all tests and so I can safely remove the instrument from the equation.
I am using the malvern specific disposable cuvettes and all the systems settings in the SOP are set to automatic so find the correct attenuator etc.
Any suggestions for going forward or any ideas of something I might be doing wrong would be greatly appreciated.
Thank you in advance!
Grace Young
I have answered this question several times. In routine experiments, the hydrodynamic radii of solid nanoparticles are easily determined by the DLS method. For micellar solutions, device developers recommend determining the size of micelles (soft matter) in the presence of a large amount of inorganic salt. They hydrate well and destroy quantum and thermal fluctuations of water. When scattering in micellar solutions, the incident monochromatic wave is split into several waves with changed frequencies ω + Δω and ω-Δω. Each splitting Δω corresponds to its own fluctuation. On the basis of light scattering by fluctuations, a theory of DLS was proposed in terms of an autocorrelation function. The scattering analysis includes, first, the determination of the constant Γ of the decreasing autocorrelation function, which is proportional to the width of the scattering spectrum and is related to the diffusion coefficient of inhomogeneities. The diffusion coefficient of inhomogeneities D, in turn, is related to their hydrodynamic diameter, which is shown by the device. All this is connected with the new theory of micelle formation, which I am developing. Quantum fluctuations in water are nonlocal, that is, they occur in all water. In addition, they are probabilistic in nature. If you are interested, read the articles
Article Structure of Micelles of Sodium Dodecyl Sulphate in Water: a...
Preprint Quantum and thermal liquid -liquid phase transitions in aque...
Hi Grace,
The quality criteria in the Zetasizer software is looking to assess the quality of a particle size measurement so I would be careful interpreting this for a sample prepared with no dispersed material.
When using filters I would usually discard the initial volume of fluid that passes through the filter as this can sometimes contain material shed by the filter, and 20nm filters are available which can greatly improve the cleanliness of your continuous phase.
Grace Young
There is no such thing as a 'blank' in DLS ('However, my water blank will not pass the quality criteria') in a similar manner that would apply to other techniques. Simply you are measuring noise when you put in a pure particle-free sample of water.
Hello Grace Young - the quality report is a list of potential reasons why the data may not be "perfect". It is likely that there are more items listed on your size quality report. The main issue is: if you have just dispersant/solvent/water then the data will be noise, it should be noise. If you repeat the measurement and overlay the correlation functions, you should notice a low intercept and a lot of randomness. So from a DLS (or size) point of view, it is not a "good" measurement. However, the amount of scattered light can still help you with your project. Every sample below the critical micelle concentration should be similarly "noisy" and of "bad quality" because there are simply not that many scattering objects in the sample. Once you pass the cmc the intensity will be stronger, and there will be enough signal to detect the size of your micelles. If you have really clean data you should be able to see the transition ("kink") in the intensity vs concentration. And at point the size should also start to become meaningful. There is an application note on this topic at
https://www.malvernpanalytical.com/en/learn/knowledge-center/application-notes/AN101104SurfactantMicelleCharacterization or https://instrumat.ch/wp-content/uploads/2016/08/Surfactant-Micelle-Characterization-AN101104-LRLL.pdf