The most advanced volumetric sorption analyzers allow surface areas as low as approximately 0.5 - 1 m² to be measured using nitrogen as the adsorptive.

With small surface areas, the quantity of adsorptive remaining in the void volume is large compared to the amount adsorbed and indeed, the void volume error can be larger than the volume adsorbed. The number of molecules left in the void volume can be reduced by using adsorptives with low vapor pressures. Beebe, Beckwith, and Honig were the first to use krypton for this purpose. Litvan reported the vapor pressure of krypton at liquid nitrogen temperature as 2.63 torr, i.e., the saturation pressure of undercooled liquid krypton at this temperature (at 77.35 K krypton is ca. 38.5 K below its triple point and solidifies at a pressure of ca. 1.6 torr). Because of this much lower saturation pressure compared to that of nitrogen, the amount of krypton remaining in the void volume, at any given relative pressure, will be much less than that for nitrogen, whereas the amount of adsorption will be only slightly less (by approximately the ratio of cross-sectional areas of nitrogen and krypton, or about 16.2/20.2). Another advantage of using adsorbents with low vapor pressure is that corrections for non-ideality are often not necessary.

Because of the very low saturation pressure of krypton at ~ 77K (i.e., 2.63 torr) the relative pressures in the classical BET range (i.e. 0.05 -0.3) correspond to absolute pressures below 1 Torr. Hence, in contrast to the experimental setup for regular nitrogen BET surface area analysis, a much more sophisticated experimental set-up is needed for krypton surface area analysis. 

In addition, at the very low pressures required for krypton analysis it may be necessary to correct for the so-called thermal transpiration phenomenon.

Different gases adsorption temp., saturation vapour pressure, cross-sectional area & scope