Hi Nesrine,

What was your sample? Was it porous?

From your file, it says 'iron' with a density of 3.4 g/cc. It does not sound very porous. If your sample is non-porous iron, the amount adsorbed of N2 at 77 K will be very very little. So I think you are observing the fluctuations due to experimental error of the machine.

As a thumb rule, you need to have at least a few m2 of sample inside the sample holder to obtain a proper isotherm. This will never work with a sample such as non-porous iron, for example.

Thanks  fermando

it is amberlite modified with iron.

amberlite itself is macroporous 

Since you have a macroporous sample, surface area should be small.

Then, the experimental results you obtained make sense.

Dear Christian Weinberger

what do you mean by equilibriation time

Fernando 

sorry , my resin is microporous not macroporous

thanks