The role of qualitative chemical analysis is well recognized by Pharmacopoeias [1] where the most of tests are intended to conform the chemical identity of the analyte as is or in a mixture. In the later case the identification is mostly based on separation and use of specific reagents. Three types of qualitative analysis are widely used in many fields. The first deals with yes/no responses according to the pre-set threshold. The second, like USP Spectrophotometry test <197> is based on profile comparison. The third referred to as sample classification [2] or discriminant analysis compares the spectral information of unknown sample within a database in order to determine which class (group) of standard is the most similar to the unknown. Reliability of the "yes/no" identification depends on sensitivity of the specific reaction. Reliability of profile comparison can be estimated in a few ways: a) as a ratio of peaks (observed in the spectrum or in the chromatogram) that can be referred according to the reference as "true" peaks to the total number of peaks; b) comparison of the profiles [3]; c) probability estimations of peak recognition as proposed in [4]. Using of models [2-4] requires existence of well characterized standards, the peaks are required to be well separated and the deviation of the peak positions should be statistically homogeneous. Identification/classification of polymorphs - compounds containing the same chemical entities, but differing by their solid state structure - requires special approach. The reasons for this are both the nature of the sample and the limitations caused by the measurement technique: a) polymorphism is a property of the solid state. Therefore, polymorphs can not be separated from their mixtures and/or from the solid matrix by traditional techniques; b) degree of crystallinity and amorphous phase content may affect the measured properties; c) on storage the polymorphs can convert to a thermodynamically more stable form; d) sample treatment (e.g. heating, irradiation, grinding or pressing ) may cause polymorphic transitions. Therefore, for example, the diffuse reflectance measurement mode is mostly used for FTIR, Raman and NIR spectroscopic experiments. e) the spectra of polymorphs show high degree of similarity. In a lot of cases the spectral regions where the differences are observed are occupied by broad, superimposed and week absorption bands. f) compendia reference standards are not available. Therefore, an "appropriate characterized" in-house primary reference standard must be established.
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