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تسجيل

Sample preparation

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  431

2026-11-14

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Sample preparation

A major advantage of IR spectroscopy is the ability to measure relatively heterogeneous materials and poorly characterised samples, particularly in condensed phases (e.g. creams, powders, crystalline materials). By their nature, these samples are often not chemically pure and IR spectroscopy can identify or confirm the existence of major constituents. IR spectroscopy is often used to demonstrate that a sample is concordant with expectation. Nevertheless, it is essential to have pure samples to act as standards for IR spectroscopy. A major difficulty can be that of purifying and handling a few micrograms of material without substantial losses, although these problems have largely been overcome by using fractional crystallisation or chromatography as a prelude to IR spectroscopy. On-line FTIR spectroscopy is possible, but is largely a research tool. Nowadays, the identification of samples in minute amounts is achieved by other techniques, such as nuclear magnetic resonance (NMR) spectrometry and mass spectrometry (MS) (see Chapter 21). This is particularly the case with hyphenated techniques, which involve the use of spectrometric methods on-line with a chromatographic process. Nevertheless, IR spectroscopy has an important role to play in identifying functional groups. FTIR is also widely used in the analysis of drugs of abuse and can be particularly useful in differentiating salt from free-base forms of a drug.