Hello Maria Gkraikioti

while it is not possible to change the measurement window, you may be able to change the "display range" quite easily. For a description of how this can be done, see https://www.materials-talks.com/solvent-peaks-how-to-get-rid-of-the-buffersaltadditive-dls-contribution/ This may be the solution to what you may be trying to accomplish.

There is also another hidden method. You could - if you are aware of the potential complications and consider yourself a light scattering expert - adjust some of the advanced analysis settings that are available in research mode. (specifically the analysis range, but again please note that this is only suitable for advanced users) https://www.materials-talks.com/advanced-research-software-features-for-the-zetasizer-nano/

Maria Gkraikioti In addition to the excellent answer (as always) from Ulf Nobbmann I would ask you what you're actually measuring, the sample preparation route, and what is the reason for trying to 'change the window'? Is this simply to reformat the axes (Ulf provides the route above) or are you only wanting to see a part of the entire sample ignoring the smaller material that (may be) is present? Changing the axes is easy. Ignoring part of the sample can be extremely dangerous or misleading. You can filter off the large material or sediment it. This changes the sample by selectively removing some of it.

BTW, and a very important point, you are not counting particles in DLS. It's an ensemble method. The system does not measure or need to know the numbers of particles for a measurement or analysis.

I am counting Fe2O3 nano clusters in water. From my previous measurements i know that in the lower or the higher nm I don't have any picks, and the size of the nano clusters is 80-100nm. So i want to narrow the window to have i clearer view of the area that concerns me and minimise the time of each measurement.

Maria Gkraikioti You are not counting nanoclusters with DLS. The most robust parameters (from the international standards) are the z-average and the polydispersity index. This isn't number of particles...

How do you know that you don't have higher or lower peaks? You haven't posted a single result. How was your system filtered? How was the sample prepared? What stabilizers and surfactants are present? DLS relies on measuring the random Brownian motion of all the particles in the system (i.e.an ensemble measurement). You can't reduce the time of measurement in the way you envision. If you have a small amount of large particles, you may want or need to increase the time of measurement. For systems your size then 30 - 60 seconds is probably sufficient.