To get an accurate measurement, you need a high ratio between the adsorbed volume in the sample and the dead volume of your system. The lower the system volume, the easier it is for the pressure sensors to notice the pressure decrease due to adsorption (a more marked decrease). In the best volumetric adsorbers, experimentally measured dead volume in the manifold is around 20-50 mL, let's say we want that an amount of sample that adsorbs 2 mL of gas (that is, around 10% of the total volume) in monolayer, then we need to have (in N2 adsorption at 77K, area is 1 molecule is 0.162 nm2) around 12 m2 loaded in the sample cell... that is the origin of the rule of thumb of at least load 10 m2.

On the other side, we don't want too much more than this amount, since it will make the analysis too long, because too many injections are needed to reach each equilibrium point.

If your material has lower surface area, then you need to have material in higher quantity. For higher surface area material, you can use less material. Since instrument measure the surface area wrt per unit mass of the sample. Best of my knowledge this is due to measurement capabilities of instrument and there is no other logic behind this. 

This is all about accuracy. 10 m2 is an arbitrary value as you can guess, as it is easy to have a uncertainty of +/- a few m2 with this kind of measurement. Therefore, 10 m2 appeared to be a minimum value to be reached. However, if you have a lower surface area, and if the results are reproducible, it is OK. If you are aware that your surface area is very low (because the material is non-porous, for example), try to weigh a high amount in your sample holder, for minimizing the absolute uncertainty. Or use another gas as adsorbate, such as krypton.

Alain

Depends on the surface area of your tested material. And I also find that: if the mass of your sample is not enough and this sample presents a lower surface area, the experimental results might be zero. Generally, we will add enough samples in the case of this sample is really enough.

Best regards!

Zhenjiang

To get an accurate measurement, you need a high ratio between the adsorbed volume in the sample and the dead volume of your system. The lower the system volume, the easier it is for the pressure sensors to notice the pressure decrease due to adsorption (a more marked decrease). In the best volumetric adsorbers, experimentally measured dead volume in the manifold is around 20-50 mL, let's say we want that an amount of sample that adsorbs 2 mL of gas (that is, around 10% of the total volume) in monolayer, then we need to have (in N2 adsorption at 77K, area is 1 molecule is 0.162 nm2) around 12 m2 loaded in the sample cell... that is the origin of the rule of thumb of at least load 10 m2.

On the other side, we don't want too much more than this amount, since it will make the analysis too long, because too many injections are needed to reach each equilibrium point.