FTIR and NIR Spectroscopy
Introduction and Principle of FTIR Fourier Transform Infrared spectroscopy measures the absorption of infrared radiation, typically across the wavenumber...
Introduction and Principle of FTIR
Fourier Transform Infrared spectroscopy measures the absorption of infrared radiation, typically across the wavenumber range of four thousand to four hundred reciprocal centimetres, arising from vibrational transitions within molecular bonds. Because each functional group exhibits a characteristic absorption frequency governed by bond strength and the mass of the constituent atoms, the resulting spectrum provides a molecular fingerprint that is highly diagnostic of chemical structure. FTIR is consequently indispensable for identity testing of active pharmaceutical ingredients and excipients, for characterisation of polymorphic and solvate forms, for assessment of excipient compatibility during preformulation studies, and for the detection of counterfeit pharmaceutical products.
Sample Preparation Techniques and NIR Spectroscopy
Sample presentation for FTIR analysis may be accomplished through several established techniques. The potassium bromide disc method involves intimately mixing the sample with dry potassium bromide and compressing the mixture into a transparent pellet under high pressure, a technique traditionally applied for assay and impurity profiling of solid samples. Attenuated total reflectance permits direct measurement of solid or liquid samples placed in contact with a high refractive index crystal such as diamond or zinc selenide, offering the advantage of minimal sample preparation. The Nujol mull technique involves grinding the sample with mineral oil and mounting the paste between sodium chloride plates, while the solution technique dissolves the sample in an infrared-transparent solvent for measurement in dedicated liquid cells. Near Infrared spectroscopy, operating at wavelengths longer than those of the mid-infrared region, exploits overtone and combination vibrational bands and has gained considerable importance as a rapid, non-destructive process analytical technology tool for real-time monitoring of blending, granulation, and content uniformity during pharmaceutical manufacturing.