Planinsek Odon, Buckton Graham
Department of Pharmaceutics, School of Pharmacy, University of London, 29-39 Brunswick Square, London WC 1N 1AX, United Kingdom.
J Pharm Sci. 2003 Jun;92(6):1286-94. doi: 10.1002/jps.10394.
The use of inverse gas chromatography to assess surface properties of a range of pharmaceutical powders was examined. The powders were two sources of hydroxy propylmethyl cellulose (HPMC), microcrystalline cellulose, magnesium stearate, and acyclovir. These were selected to cover a range for properties from amorphous to crystalline, hydrophilic to hydrophobic, and high to low aqueous solubility. It was found that many powders gave a similar value for the dispersive surface energy, which is surprising given the differences in chemical nature. It is likely that this is due to the use of infinite dilution giving rise to the study of specific regions of the powder surface only. The values obtained for dispersive energies were not influenced by packing mass or flow rate of the carrier gas. The retention of polar probes on the column was a concern for the amorphous HPMC samples. This gave rise to derived values for acid-base nature which varied depending on sample mass and carrier gas flow rate. The data show that care must be taken when studying amorphous samples for which it is possible to obtain diffusion into the material rather than just surface adsorption of probes. Despite these problems, it was still possible to differentiate between the samples (including differences between the two HPMC samples) by use of polar probes. It was also possible to see differences in absorption into the sample, reflecting the different physical forms. For example, microcrystalline cellulose behaved very differently to HPMC. It can be concluded that inverse gas chromatography is a valuable characterization tool, but it must be used with care especially with respect to polar probes on amorphous samples.
考察了用反相气相色谱法评估一系列药用粉末表面性质的情况。这些粉末包括两种羟丙基甲基纤维素（HPMC）来源、微晶纤维素、硬脂酸镁和阿昔洛韦。选择这些粉末是为了涵盖从无定形到结晶、从亲水性到疏水性以及从高到低水溶性的一系列性质。结果发现，许多粉末的分散表面能值相似，鉴于其化学性质的差异，这一结果令人惊讶。这可能是由于采用无限稀释法仅对粉末表面的特定区域进行研究所致。所获得的分散能值不受填充质量或载气流量的影响。对于无定形HPMC样品，极性探针在柱上的保留是一个问题。这导致了酸碱性质的衍生值因样品质量和载气流量而异。数据表明，在研究无定形样品时必须小心，因为有可能发生探针扩散到材料中，而不仅仅是表面吸附。尽管存在这些问题，但通过使用极性探针仍有可能区分样品（包括两种HPMC样品之间的差异）。还可以看出样品吸收的差异，这反映了不同的物理形式。例如，微晶纤维素与HPMC的行为非常不同。可以得出结论，反相气相色谱法是一种有价值的表征工具，但必须谨慎使用，尤其是对于无定形样品上的极性探针。
