Thank you Dear Rogiers  for your contribution. It seems like interesting and I think  the most important thing is accuracy in this method.

you can use Master Sizer apparatus or dry-sieving method.

Thank you Dear Hedie for contribution. 

I hope this attachment will help you solve the problem.

Thank you Dear Bashir for your interest.

In our lab we use a Mastersizer from Malvern. As you can find in the literature and as our results have also shown, there could be a difference in the clay fraction derived from the two different techniques.

Thank you Dear Hunziker. 

Bouyocos Hydrometer method after Gee and Bauder

       Perhaps a better question is whether we should continue measuring the particle size distribution... Why is that distribution useful? We keep measuring it, as if it contributed useful information, but in fact, we know that very few properties of soils actually depend on it. Most properties of soils that we are interested in are related to the structure of soils, much more than to their granulometry. Most attempts, for example with pedotransfer functions, to derive useful data out of the PSD have failed, or are unsatisfactory. So we should ask instead what new methods have been developed recently to measure soil physical properties directly...

Thank you Dear Philippe for valuable conteptional approach. 

Particle size distribution is useful for understanding potential exposure as smaller particles are more likely to be inhaled or ingested  (childrens hand to mouth contact). We also use a Malvern and I have been very pleased with the results.

Thank you dear Suzette for your contribution.

@Suzette

Which Malvern sizer? The ones I know measure micron-size and up

Thank you dear Harry for valuable contribution. 

As all we know that soil particle diameter size classified at as below.

Name of soil separate Diameter limits (mm) (USDA classification)

Was not aware of the latest Malvern sizer but I would be skeptical on the lower limit of 10 nm because optical signals scale with diameter to the 6th power for particles smaller than the probe light (typically several 100 nm).

The specs, also, mention that the lower detection limit depends on preparation of the sample. I would trust DLS and in the dry phase the SMPS

I find it really interesting that whenever one asks the question "Why are we doing this?", the question is labelled as conceptual or philosophical, then one moves on as if nothing had happened... Yet, I still think that in many circumstances where people think they are getting valuable information by measuring the particle size distribution, that parameter actually carries no information whatsoever. Take the case mentioned by Suzette Morman, 

Dear Harry, Thank you very much again for your contribution. I haven't been used this devices so far really. So, I have no idea working principles of its. Actually, both accuracy and working range is very important in any scientifical method by using any devices.

 Here, I hope that someone who has experience in this devices will explain the skeptical condition which is you expressed.

Dear Philippe, thank you so much for your interest really. In the your first answer, it was claimed that "Why is that distribution useful? We keep measuring it, as if it contributed useful information" . So as I inferred that it is not useful contrary to popular belief. Answer was might labelled as philosophical because of without any evidence as reference given.

So, All we know that PSD affects soil physical, chemical and biological properties and also affects whole plants health in the terrestrial ecosystems. There are lots of study strongly support if we search it out.

So, whats your evidence as reference related to your claims (PSD less important than structure like that)?

For analysing the sizes of dust particles, we take electronic microscopic pictures and measure the diameter of single particle with photo processing software.  

Thank you Dear Lian for your contribution.  If you don't mind, may you share any study you did including this method?

Ugur,

      To answer your penultimate comment (starting with Dear Philippe...), I am not making claims. There is so much evidence, it is hard to know where to start. We know from basic soil physics (and people have documented for the last half century) that the granulometry of a soil does not at all determine its hydraulic conductivity. The way the particles are organized (i.e., the structure of the soil) strongly influences that parameter. For example, a soil can be 95% kaolinite clay (as some oxisols in the tropics are) and have the hydraulic conductivity of a sand. That has been well demonstrated (for example by Professor Ricardo Radulovich and me). In addition, any earthworm activity could create a macroporosity that will have a huge effect on the hydraulic conductivity as well... None of that is reflected in the granulometry. The amount of clay may determine the sorptive capacity of soils, but if all the clay surfaces are covered with organic matter (e.g., humid acids), the effect of the clay fraction may be hidden... So, before one measures the PSD, it is important to know what one wants to do with that information, and whether it makes sense... We should stop measuring things just because we can...

Please see the attached file as reference.

Dear Philippe,

First of all, thank you very much  for your comments.

Your answer which is two penultimate including sharp-sighted as I mentioned before that I inferred it is not useful contrary to popular belief. Now I understand your perspective. But as far as I am concerned that we should consider that there are lots of different ecosystem on the earth. Also, all we know that soil substance consist of many of parameters (phsical, chemical and biological) affecting one another. And also consider that in one ecosystem, while one soil parameter have other fish to fry,  in the other ecosystem the any other soil parameter will be outweigh than others...