Direct derivation of the crystalline fraction of highly potent active pharmaceutical ingredients by X-ray powder diffraction.

Direct derivation (DD) is a novel Powder X-ray diffraction quantification method based on intensity-composition equation, which can determine the weight fraction of individual phases in a mixture of components by chemical formulas . The DD method was applied to determine crystallinity degree of binary mixtures containing amorphous hydroxypropyl methylcellulose and crystalline monohydrate α-lactose in weight percentage ≤ 15% w/w. Three different scenarios were considered: a) the unit cell parameters of the crystalline phases are available b) the unit cell parameters are unknown but the patterns of pure crystalline and amorphous references are available and c) only the mixtures' patterns are available. Relative errors in scenarios a and b were comparable and reasonable (<20%), while in c, the crystalline degree was clearly underestimated evidencing the importance of determining the maximum number of crystalline reflections This can be easily achieved when the unit cell parameters and/or the patterns of pure references are available. To simulate the quantification of high potent API, the method was evaluated considering the scenario b, in samples covered by Kapton® film as containment system. In this case, an accurate quantification was achieved by subtracting the film signal from the observed pattern.

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