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N 10 March 2015 Tablets & Capsules analysis Applications of NIR spectroscopy in assessing raw materials and solid dosage forms Thomas B. Gold Metrics Contract Services This article summarizes the principals of near-infrared (NIR) analysis and discusses how it has been applied to evaluate raw materials and finished products, including correlating NIR and dissolution testing results. sample for FTIR spectroscopy involves diluting it and combining it with a pellet of potassium bromide (KBr) or a mull of Nujol, which is a heavy mineral oil with an uncomplicated IR spectrum. Both compounds are ionic and will typically not generate peaks in the FTIR range, whose fundamental frequency vibrations lie between 400 and 4,000 reciprocal centimeters (cm -1 ). NIR spectroscopy looks at the higher energy states of vibrations—known as overtones—and at combination bands of the fundamental vibrations that are observed in the mid-range IR region. These overtones occur between 4,000 and 12,500 cm -1 , which is roughly two to three times the frequency of the fundamental vibrations. The stretching of nitrogen-hydrogen (N-H), carbon-hydro- gen (C-H), and oxygen-hydrogen (O-H) bonds produces absorption bands in the NIR region; the absorption intensity decreases and the band broadens as the over- tones increase. It is the lower intensity of absorption that allows direct NIR analysis of samples, eliminating the dilution step that FTIR requires. In fact, modern NIR analyzers incorporate Fourier transform, which enables them to give superior resolution over the earlier dispersive NIR instruments. IR spectroscopy has established itself in the pharma- ceutical industry as a core analytical tool for quantitative and qualitative analysis of raw materials, finished prod- ucts, and in-process samples. The power of NIR lies in its non-invasive and non-destructive methodology and its ability to extract product-specific information relatively quickly. There are three spectroscopic methods used to observe molecular vibrations: Mid-range infrared, near infrared, and Raman. Mid-range infrared, more com- monly called Fourier transform infrared (FTIR) is widely used to identify materials. It looks at fundamental molec- ular vibrations and the transition that occurs from the vibrational ground state to an excited state. There is inherent selectivity with FTIR because the fundamental vibrations give rise to strong absorbance. Preparing a

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