Identification of raw materials and pharmaceutical preparations

Control analyses rely on the use of appropriate procedures or measurements allowing the identity of the materials involved in each step of the manufacturing process from receipt of raw materials to delivery of the finished products to be assured. NIR spectroscopy is an advantageous alternative to wet chemical methods and instrumental techniques such as IR, Raman and nuclear magnetic resonance (NMR) spectroscopies. 

One other important consideration in constructing a library is checking that all spectra are correct. This can be done by visual inspection of the spectra and outlier detection tools. For various reasons (e.g. an inadequately filled cuvette, large temperature fluctuations), spectra may differ from others due to factors other than natural variability. Any such spectra should be excluded from the library. Spectral libraries are used for two different purposes, namely identification (of chemical structure) and qualification (of chemical and physical attributes). 

This involves the confirmation of a certain chemical entity from its spectrum by matching against the components of a spectral library using an appropriate measure of similarity such as the correlation coefficient,6 23 also known as the spectral match value (SMV). SMV is the cosine of the angle formed by the vectors of the spectrum for the sample and the average spectrum for each product included in the library. 

Distance-based methods possess a superior discriminating power and allow highly similar compounds (e.g. substances with different particle sizes or purity grades, products from different manufacturers) to be distinguished. One other choice for classification purposes is the residual variance, which is a variant of Soft Independent Modeling of Class Analogy (SIMCA). 

Analyte Pattern recognition method Remarks References 

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