However, with krypton adsorption this effect commences at higher adsorption pressures and it is possible to calculate BET surface area which better represents the true surface area of the material. BET surface area via nitrogen adsorption is shown to be erroneously high due to a structural swelling and adsorbate encapsulation effect occurring throughout the BET range and which should preclude the use of BET theory. In this paper, four commercial magnesium stearate materials in mono- and di-hydrated forms are analysed by nitrogen and krypton adsorption for the calculation of BET surface area. Magnesium stearate is an extremely common pharmaceutical excipient and the measurement of BET surface area via nitrogen adsorption is undertaken during pharmaceutical formulation and manufacture.
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