at the first glance, I would like to ask: do you have enough colloidal dispersion amount, can you prepare any amount, or you only have 1 sample, and that's it? Or do you want to develop a routine analysis method for later use when you are preparing more and more batches?

In case you have enough and want to develop a method, I suggest to evaporate enough liquid and measure the remaining solid content with an analytical balance with micrograms resolution.

In parallel, you take UV-VIS spectra of those colloidal liquids and determine which absorption peak could be useful, then you calibrate.

for later use as an analytical method, you simply use that absorption peak.

Dear Dr. Wessling,

Thanks a lot for your good suggestion.

I have a colloidal sample with a volume of about the 25 ml that may approximately contain a few micrograms of a semiconductor material in the form of nanoparticles. In addition, I need the original sample for another characterization analysis and I prefer to use a method for measuring the concentration of the colloid that is not changing the volume of it.

it's hard to help with so little information, so I ask some more:

- did you make this colloidal sample yourself?

- can you repeat it? can you prepare comparable colloidal systems for comparison?

- what is the UV-VIS spectrum like?

Maybe then you can establish a calibration curve and measure the absorption strength of the sample you want to analyze?

Yes. I did. It is possible for me to fabricate the another sample but this work is expensive and I do not want to repeat this process. In fact, this amount of the colloid is adequate for performing the other analysis. The UV-VIS spectrum of the colloid shows a gradual increase in the absorbance with decreasing the wavelength from the onset wavelength of 350 nm.

I think that the best idea is measure the UV spectra, you can use a special cell with few microlitters to not modified the original concentration.

Ashkan, from your comment I would conclude there is no peak? can you show the spectrum here for everybody how is followiong?

is the colloidal system transparent? (or is it hazy?)

what is the particle size measured by Laser-Doppler or other methods?

Yes. The colloid is approximately colorless and no analysis has been done on measuring the size of nanoparticles.

If chemical composition of nanoparticlesare known, you may use "atomic absorption spectroscopy" method...

Askan, "colourless" is one characteristic, but I want to know: is it transparent or hazy?

Oleg: for AAS, also standards would have to be made, and I am afraid that his concentration may be too low for AAS as well ...

Dr. Wessling, You're right. However, according to the absorption spectrum it can be concluded that the material is transparent, meaning there is no appreciable absorption in the visible spectrum that making the colloid transparent.

If you define chemical composition, we can estimate the concentration limits for AAS method. Standarts may be prepared by using pure elements...

And if AAS method will be not sensitive, we may say that concentration less then...

Askan, you may still misunderstand me: is the colloidal dispersion transparent clear? Does it look like water? Or like dilute milk?

Dr. Wessling, I gave you the answer clearly. The colloid looks like water (colorless and is not shown appreciable absorption in the visible spectrum ).

Dear Dr. Tolochko,

Thanks a lot for your suggestion.

The colloid consists of a small amount of the silicon nanoparticles (Its value can be estimated about the micrograms) that is dispersed in the 20 ml of Ethanol.

Ashkan, may I ask: did you resolve the problem you had? was any of the various suggestions here helpful for you?

Dr Wessling,

I could prepare a colloidal sample with concentration of the 0.1 C0 (Co is the concentration of original sample) and take its UV-VIS spectrum. Can I measure the concentration of the colloid by comparing the UV-VIS spectra of these 2 samples?

you somehow need to calibrate! (you don't know the concentration of the original sample, right?) I would suggest to evaporate your 0.1 C0 sample, take more spectra (for determined evaporation steps, so you need to know what will be the relative concentration), then finally you dry completely and weigh the remaining material using a highly sensitive analytical balance. That way you may appoach a relatively reliale guess of your C0 concentration.

Yes. I don't know the concentration of the original sample. I just like to find it! I'll do your proposed process. I hope that the amount of remaining material is within the precision of our balance (10 microgram). If the sample volume is about the 5 ml, do you think five evaporation steps are enough for this process?

Thanks a lot for your useful Guidelines.