Hi all,
I have to run an experiment comparing NTA and DLS performances, sizing samples composed of two different population of polystyrene particels (200 nm and 2 um) mixed in different ratios.
I know how tricky is size these samples with these wide dimensions differences and that the light scattering of bigger partiles would probably hide the small ones, moreover will be difficoult to select an appropriate camera level and laser wavelength for NTA that allow to track properly the two populations,
I was thus wondering which could be the best experiment settings for try to size them, if someone has experience of analysis of such samples.
Thank you so much
Gabriele Vella
At these sizes (200/2000 nm) I'd be using laser diffraction, not DLS, as my preferred light scattering technique. NTA is a number counter. You're not indicating whether you require a number or volume distribution and the approximate proportions. There's a 10-fold difference in diameter which translates to a 1000-fold difference in volume/mass and 10^6 difference in intensity (DLS). If you're trying to count the particles under NTA then you'd need to calculate what concentrations produce equal numbers of the different sized particles. You'll need a thousand times more mass of the larger ones to give the same number of the particles of the smaller ones... This, of course, means that a volume distribution would be difficult in this context...
Gabriele Vella
Are you on vacation or ill? If the latter, we wish you a speedy recovery. If the former, then enjoy your time off and we'll hear from you in September...
Hi Gabriele Vella : For the DLS part, you may find a Mie scattering calculator (for example described in https://www.materials-talks.com/blog/2017/03/07/can-i-use-dls-for-xyz/ ) of interest. It can predict how much light per particle - based on scattering angle and optical properties - different particle sizes will scatter.
Here is an example from 200nm to 2 microns, HeNe laser, backscattering, polystyrene in water
Thank you everybody for the answer and tips and sorry for the delay in thanking each one of you,
this experiment was part of a wider work in pushing and testing the capability of several techniques in sizing and quantifying (concentration calculated in weight for volume) of particles in wide dimensional ranges,
for NTA, using our instrument with his equipment and his blue laser, despite our attempts to set the best settings possible for these measurement, also the analysis of a 1 um polystyrene standard was impossible to conduct, giving us unrealistic and unreliable results,
for this reason we didn't go ahead with the mixtures,
anyway I'll make you aware of the outcomes of the whole work,
thank you so much again
- Badges
- Science method