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The basic interferometer unit is shown in figure 32. This unit is the central device round which the modular system is built. It consists of Beam Splitter that accepts the light output from the source and sample unit and directs it into the interferometer and out again via two corner cube mirrors.
The light from the interferometer leaves the Beam Splitter and enters the sensor module that reads the Interferogram so produced. The interferometer unit also contains its own power supply and amplifier and the laser.
The Optical System of the Interferometer Unit
The optical system of the interferometer unit is shown in figure 34.
Light passes directly to the Beam Splitter where 50% passes through and is reflected back, by means of the two corner cubes and the retro prism reflector, to the Beam Splitter where the beam is split again in half and 25% passes to the sensor. The half of the incident light that is reflected by the splitter passes to the movable corner reflector only and then back to the Beam Splitter where half (25%) of the original incident beam also passes to the sensor. It is clear that the optical system is very neat and compact.
The unique character of the optical system resides in the use of the cube mirrors.
The Light Source
The light source is a separate component and a diagram of the optical system is shown in figure 35.
The light source is seen to consist of a suitable lamp and a parabolic mirror that directs a parallel beam of light out of the unit and which is suitably housed as a separate unit that can be directly connected to the interferometer unit.
The light source usually contains the sample cell or appropriate sample system. Thus, there will be a range of different light sources with sampling devices available from which the most appropriate can be selected.
The Sensor System
The sensor system is also designed to be a single compact unique module that is compatible with the interferometer module. A diagram of sensor unit is shown in figure 36. The sensor unit again in modular form consists of a parabolic mirror and suitable sensor that may be a simple light sensing device such as a photocell or a photomultiplier or a Diode Array. These sensor units also fit directly and easily to the interferometer unit.
There is large number of FTIR instruments available and most manufacturers will be pleased to demonstrate their equipment and run a sample. An instrument will be a significant investment to many companies and therefore the choice should be made with considerable care and circumspection.
About the Author
RAYMOND PETER WILLIAM SCOTT was born on June 20 1924 in Erith, Kent, UK. He studied at the University of London, obtaining his B.Sc. degree in 1946 and his D.Sc. degree in 1960. After spending more than a decade at Benzole Producers, Ltd. Where he became head of the Physical Chemistry Laboratory, he moved to Unilever Research Laboratories as Manager of their Physical Chemistry department. In 1969 he became Director of Physical Chemistry at Hoffmann-La Roche, Nutley, NJ, U.S.A. and subsequently accepted the position of Director of the Applied Research Department at the Perkin-Elmer Corporation, Norwalk, CT, U.S.A.
In 1986 he became an independent consultant and was appointed Visiting Professor at Georgetown
University, Washington, DC, U.S.A. and at Berkbeck College of the University of London; in 1986 he retired but continues to write technical books dealing with various aspects of physical chemistry and physical chemical techniques. Dr. Scott has authored or co-authored over 200 peer reviewed scientific papers and authored, co-authored or edited over thirty books on various aspects of physical and analytical chemistry. Dr. Scott was a founding member of the British chromatography Society and received the American Chemical society Award in chromatography (1977), the M. S. Tswett chromatography Medal (1978), the Tswett chromatography Medal U.S.S.R., (1979), the A. J. P. Martin chromatography Award (1982) and the Royal Society of Chemistry Award in Analysis and Instrumentation (1988).
Dr. Scott’s activities in gas chromatography started at the inception of the technique, inventing the Heat of Combustion Detector (the precursor of the Flame Ionization Detector), pioneered work on high sensitivity detectors, high efficiency columns and presented fundamental treatments of the relationship between the theory and practice of the technique. He established the viability of the moving bed continuous preparative gas chromatography, examined both theoretically and experimentally those factors that controlled dispersion in packed beds and helped establish the gas chromatograph as a process monitoring instrument. Dr. Scott took and active part in the renaissance of liquid chromatography, was involved in the development of high performance liquid chromatography and invented the wire transport detector. He invented the liquid chromatography mass spectrometry transport interface, introduced micro-bore liquid chromatography columns and used them to provide columns of 750,000 theoretical plates and liquid chromatography separations in less than a second. Dr. Scott has always been a “hands-on” scientist with a remarkable record of accomplishments in chromatography ranging from hardware design to the development of fundamental theory. He has never shied away from questioning “conventional wisdom” and his original approach to problems has often produced significant breakthroughs.