Hello,

In very short, answer to your question is- The Z average is the intensity weighted mean hydrodynamic size of the ensemble collection of particles measured by dynamic light scattering (DLS). The Z average is derived from a Cumulants analysis of the measured correlation curve, wherein a single particle size is assumed and a single exponential fit is applied to the autocorrelation function.

In exponential fitting expression (attached below), I is the scattering intensity, t is the initial time, τis the delay time, A is the amplitude or intercept of the correlation function, B is the baseline, D is the diffusion coefficient, q is the scattering vector, λo is the vacuum laser wavelength, ñ is the medium refractive index, θ is the scattering angle, k is the Boltzmann constant, T is the absolute temperature, η is the viscosity of the medium, and RH is the hydrodynamic radius.

Equation for same is hereby attached.

Priyadarshi Aparajay

Not sure what you're doing here but there are plenty of suspicious indications in the report you attached - a narrow peak like this is only expected for a particle size standard. Have you run a standard (e.g. 60 nm) in the system to confirm performance? The report says 'Refer to Quality Report'. What does the quality report say? Why are you using manual and not automatic settings (what have you changed)? Why are you diluting an emulsion in DI water and not the mother liquor (DI water is likely to destabilize the system)?

To what extent have you filtered the system/continuous phases? I'd expect 0.2 or 0.02 microns or better... A large z-average in comparison to the main peak is usually an indication of contamination. The attenuator setting of 11 and the position (4.65 mm) shows that you have no particles in the system. You need to increase the concentration by a factor of 1000 or 10000.

And that's the start. Please attach the raw data file (*.dls) rather than a scan of the report and we can be far more specific in comments.

Alan F Rawle Hello, I would like to ask, why "The attenuator setting of 11 and the position (4.65 mm) shows that you have no particles in the system."? I have nanoparticles with size

Wiktoria Matyjasik

For a DLS experiment at least of 3 parameters needs to be working for you to get sufficient scattering for a robust result:

• Size. Smaller particles scatter weakly in proportion to 1/(volume)2
• Concentration - typically (not in the multiple scattering region), doubling the concentration will double the intensity
• Optical contrast (or relative refractive index). For example, metal colloids will scatter much more strongly than proteins of the same size

Attenuator 11 suggests that the amount of scattering is very weak. The ideal setting would be 7 but, as you've found, you can get results outside this value. Robust results are important. Take note of the suggestions in the Quality report. This report is an excellent guide to what may be awry in any DLS experiment. I would try repeating your results that you've obtained on Attenuator 11 with higher concentrations (100 - 1000 times). The international standards (ISO and ASTM) recommend a concentration ladder to isolate good concentrations for stable measurement.

DLS is an excellent screening device as you say. Take care with comparing DLS (intensity) with TEM (number) distributions. Take care with your TEM sample preparation as the results are invariably affected by this.

Priyadarshi Aparajay

Now what material has a RI of 1.10? On your attached report.