X-ray powder diffraction can be used to characterize substances with a crystalline composition. For each crystalline substance there is an unique diffractogram, which is also the result of this method and allows further qualitative analysis.
In my diploma work, I analysed nineteen samples of antidepressants with the computer programs X’Pert HighScore Plus, CSM, ConQuest, CSD and Mercury. With the X’Pert HighScore Plus program, I compared the samples with each other and obtained data on the present crystalline and amorphous phases. I have found that some diffraction patterns with the same active substance are similar to each other, but some are also different. This means that they contain different auxiliary substances. Medicines containing smaller proportions of active substance may match with the peaks of the same auxiliary substance. One of the main purposes was to identify substances in samples and compare them with the substances listed in the declaration. The identification of the compounds was made using the CSM program. ConQuest program, CSD and Mercury were used to determine active substances that the CSM program could not determine. Due to too small a proportion or the presence of amorphous phase, I was unable to identify some active substances and auxiliary substances in the samples. Listed sample declarations and identified substances, as expected, matched each other.
I was also interested what fraction of the tablet the active substance represents and what is the fraction of the auxiliary substances. Therefore I weighed all the samples on an analytical balance and calculated the mass fractions from the obtained masses and known masses of active substances. As a result, I found that the higher the mass fraction of the substance in the tablet, the better the peaks of the substance are resolved in the diffraction patterns.
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