Abstract

Improved measurement of powder wettability with the Washburn-Direct method – A reproducibility study based on measurements of the water wettability of microcrystalline cellulose powder

In pharmaceutical analysis, adsorption measurements on powders using the Washburn method are part of the standard repertoire. In application, however, this method is demanding, often subject to a large measurement uncertainty, and associated with some potential sources of error. Particularly sensitive are the preparation of homogeneous samples with always the same packing density and the evaluation of the measurement curve. In this article, possibilities are presented to reduce the influence of these 2 sources of error and to achieve more user-independent, better reproducible results. The new evaluation method Washburn Direct presented here shows the measurement value sought – the capillarity constant or the contact angle – directly on the basis of a plateau value in the measurement curve. This plateau can be taken from the curve more reliably than the slope of a linear range to be determined in classical Washburn plotting. In addition, possible inhomogeneity of a sample becomes immediately visible, which leads to a clear assessment of the evaluability of the measurement data in principle. As a further influencing factor, the uniformity of the powder packaging is ensured by a preparation set that is also presented. The good reproducibility of the powders prepared in this way and of the Washburn Direct evaluations is demonstrated by the reproducibility of measurements on microcrystalline cellulose.

Korrespondenz:

Dr. Daniel Frese, Krüss GmbH, Borsteler Chaussee 85, 22453 Hamburg (Germany), E-Mail: d.frese@kruss.de