MCA Services, Unit 1A Long Barn, North End, Meldreth, Cambridgeshire, UK.
MCA Services, Unit 1A Long Barn, North End, Meldreth, Cambridgeshire, UK.
Int J Pharm. 2019 Sep 10;568:118522. doi: 10.1016/j.ijpharm.2019.118522. Epub 2019 Jul 15.
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. 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. 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. 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. The disparity between nitrogen and krypton adsorption is greater for the di-hydrate form: the mean average BET surface area of 10 samples from the same di-hydrate containing batch are 23.18 mg via nitrogen adsorption and 6.78 mg via krypton. It is also shown than the standard deviation of BET surface area across 10 analyses of each of the four batches is considerably lower via krypton adsorption. Finally, an analytical protocol for krypton adsorption onto magnesium stearate for BET surface area measurement is established.
硬脂酸镁是一种极其常见的药物赋形剂，在药物配方和制造过程中，通过氮气吸附来测量 BET 比表面积。本文通过氮气和氪气吸附对四种商业硬脂酸镁单水和双水合物材料进行了分析，以计算 BET 比表面积。由于在 BET 范围内发生的结构膨胀和吸附物包封效应，通过氮气吸附测量的 BET 比表面积被错误地高估，这应该排除 BET 理论的使用。然而，通过氪气吸附，这种效应在更高的吸附压力下开始出现，因此有可能计算出更能代表材料真实表面积的 BET 比表面积。氮气和氪气吸附之间的差异对于双水合物形式更大：同一批双水合物中 10 个样品的平均 BET 比表面积通过氮气吸附为 23.18mg，通过氪气吸附为 6.78mg。此外，通过氪气吸附，四个批次中每个批次的 10 次 BET 比表面积分析的标准偏差明显更低。最后，建立了用于测量硬脂酸镁 BET 比表面积的氪气吸附分析方案。
