The characterization of MFI-type samples with crystals exhibiting either a homogeneous or heterogeneous distribution of the trivalent metal (aluminum or iron, labeled T(III)) is carried out using isothermal gas adsorption microcalorimetry (Ar, N2, and CO) coupled with quasi-equilibrium adsorption volumetry at 77 K. It is found that, especially during the "fluid-like’ to ’solid-like" phase transition exhibited on these samples, carbon monoxide can distinguish those with a distinct T(III) zoning (whether,it is toward the interior or exterior of the crystals). Argon however, is not greatly affected by the T(III) content (whatever the distribution) and provides a complementary textural examination of these samples.