Near-infrared light spans the 800 nm - 2.5 µm (12,500 - 4,000 cm-1) range and is energetic enough to excite overtones and combinations of molecular vibrations to higher energy levels.
NIR spectroscopy is typically used for quantitative measurement of organic functional groups, especially O-H, N-H and C=O. Detection limits are typically 0.1% and applications include pharmaceutical, agricultural, polymer and biological analysis.
Near Infrared Spectrometry - Instrumentation
The components and design of NIR instrumentation are similar to uv-vis absorption spectrometers. The light source is usually a tungsten lamp and the detector is usually a PbS solid-state detector. Sample holders can be glass or quartz and typical solvents are Carbon Tetrachloride (CCl4) and Carbon Disulfide (CS2). The convenient instrumentation of NIR spectroscopy compared to IR spectroscopy makes it much more suitable for on-line monitoring and process control.