Dakin, J.P., Mackenzie, S.J. and Hodgkinson, J.
Chapter 7. Optical fibre chemical sensing using direct spectroscopy
In Optical Fibre Sensors.
SPIE: the International Society for Optical Engineering..
Chapter 7: Introduction: It is the quantised nature of our universe, most evident at the atomic and molecular level, which allows so much information about the constituents of matter to be deduced from optical spectra. Because molecules and atoms can only emit or absorb photons (particles of light) with energies that correspond to certain allowed transitions between quantum energy states optical spectroscopy is one of the most valuable tools of the analytical chemist. It can provide a rapid non-destructive analysis of many important compounds and radicals, and optical fibres permit remote on-line monitoring. Two basic approaches are possible, either direct optical interaction with the analyte, or indirect analysis using chemical indicators; ie compounds which change their optical properties by reaction with the analyte. This chapter concentrates on the first method, that of direct spectroscopy. As stated above, the advantages are that the method is non-destructive to the sample under test and is usually very rapid. The disadvantage is that it is often not as selective as indicator chemistry, because many families of compounds exhibit similar optical properties when monitored directly.
We shall summarise the principal methods of optical spectroscopy, describe how a sensing head can be "remoted" using optical fibre probes and discuss the advantages and disadvantages of several techniques. In chapter 10, by O.Wolfbeis, the complementary indirect methods, based on optical indicators, will be considered.
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