To an outsider to the pharmaceutical industry, the notion of D-values (e.g. D10, D50, D90) being a measure of particle size and distribution is a difficult concept to accept. Basic statistics and a common understanding of distributions might dictate that, provided one is allowed to assume that the particles are relatively spherical, the most logical means of quantifying the particle size of a sample would be to use the mean diameter and standard deviation values. This method is poorly suited for two reasons however. Firstly, this assumes a normal distribution, which can be very far from the case, especially in blends of different sized materials; and secondly the results of this method would be skewed to an almost unusable degree by the sheer numbers of small particles or “fines” produced in many pharmaceutical processes.
For these reasons it is necessary to have a particle size quantification system better suited to the specific requirements of the pharmaceutical industry; and D-values, while basic, fit this requirement well.
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