Fourier-transform Infrared (FT-IR) microspectroscopy is the union of microscopy with infrared spectroscopy for the analyses of microscopic particles. The combination of microscopy and spectroscopy is extremely useful, if not mandatory, for contaminant particle examinations. Microscopy is used in selecting samples or areas within a sample for analysis, assessing the most effective and efficient spectroscopic technique, observing a sample’s micro-features, and sample preparation. Sample micro-structure may differentiate samples of similar chemical composition such as cellulosic materials such as cellulosic material such as cotton, rayon, or wood pulp paper. However, microspectroscopic examination may be used to determine the chemical composition of morphologically similar objects. For example, fibers that appear to be the same color and have similar cross-section shapes, may be colored using different dyes, which microspectroscopy could identify and differentiate. The symbiotic relationship between microscopy and spectroscopy requires the particle analyst be well versed in both microscopy and spectroscopy. We employ several employees with appropriate expertise and experience. Fourier-transform infrared (FT-IR) spectroscopy is a widely used analytical tool in chemical analyses. Infrared spectroscopy provides information regarding the chemical bonds of a sample, and most people consider it as a tool mainly for chemical identification. However, infrared spectroscopy is also quite useful in the identification of polymorphs, and in the analysis of specialized drug substrates, such as chemical coating on arterial stents.
Polymorphs are compounds that are identical chemically but arranged in different crystalline packings within the unit cell. Some polymorphs, such as hydrates and solvates, differ in that a solvent molecule is introduced into the structure. Amorphous materials are also included in this description. Even though an infrared spectrum is based upon chemical bonds and their associated motions (e.g. bends and stretches), certain infrared bands are also sensitive to the overall environment. The different crystalline packings in polymorphs result in slightly different chemical environments for each molecule, and some types of bonds, such as carbonyl bonds, are quite sensitive to this environment. The result is a shift in the carbonyl stretch, and usually other bands as well. Solvates and hydrates typically will exhibit even greater differences, with new bands due to the solvent appearing in the spectrum. Polar functional groups such as OH absorb quite strongly in the infrared region, and therefore infrared spectroscopy is quite useful in characterizing solvates and hydrates with this functional group. For example, crystalline hydrates typically have an OH stretching band at 3650 ± 40 cm-1. Even amorphous materials will exhibit changes in the infrared spectrum, as compared to the crystalline material. Typically, a spectrum of an amorphous material will exhibit band broadening of certain vibrational modes, due to the random orientation, and therefore random chemical environment within the sample.
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