Raman spectroscopy is emerging as a leading technique for on-line analysis and measurement, since it is versatile and can be used in a wide range of media. A recent paper (Clegg I M et all, Appl Spectroscopy, 2001, 55, 1138) lists the valuable practical aspects of the technique as:

• The interface to the process can be easily accomplished. In normal practice it is a non-contacting backscattering technique, i.e. access is only needed to one side of a sample. Therefore, measurement probes can be simply inserted into process lines or vessels. Conversely, a probe can be inserted in a sampling loop or can be made available in an analysis station located near to the source of samples.
• Many sample types can be analysed. Solids, liquids, and gases can be analysed directly as they are produced so that little or no preparation is required. Mixed phase systems such as emulsions, suspensions, dispersions, and slurries can also be analysed directly.
• There is minimal intrusion to the process. Glass is a weak Raman scatterer, so we can easily obtain spectra through windows or sight glasses or even through the wall of glass vessels such as reaction flasks.
• The spectrometer can be easily protected. The signals can be readily conducted through standard optical fibres so the spectrometer can be housed some distance from the process where it can be protected in a closely controlled environment.
• Hazardous samples can be readily sampled. The ability to "look" through a window means that it is environmentally robust. Sample under vacuum, at high pressure, at low or high temperatures, or in chemically hazardous environments pose no insurmountable problems.