Specialising in custom-designed, precision scientific instruments, built, programmed and calibrated to the most exacting standards. The range includes precision dataloging barographs, with built-in statistical analysis, Barographic Transient Event Recorders and computer-interfaced detectors and sensors for environmental monitoring & process control.
A site dedicated to scientific techniques, experimental methods, & investigative tools for the inventor, researcher and laboratory pioneer. Articles on glassblowing, electronics, metalcasting, magnetic measurements with new material added continually. Check it out! www.drkfs.net
click on any item in the list for its wikipedia entry if available.
A diagram of the grating IR spectrometer is shown in figure 9.
Light from the IR source is reflected from a mirror, through the reference cell, through an attenuator system and onto a second mirror, By imposing a simple device in the path of the reference light beam that removes a continuous. but controllable, fraction of the light allows the reference beam to be attenuated. The attenuator can take the form of a comb, the teeth of which are cut so that the amount of light attenuated is linearly related to the lateral movement of the comb through the beam. After passing through the attenuator to the second mirror, the attenuated light passes through a chopper. The chopper has reflecting and transmitting surfaces and, thus, alternately allows light to pass from the reference cell to the grating and then light from the sample cell to the grating. At the grating light of a specific wavelength is selected to pass to the IR detector.
As a consequence, the chopper arranges for the sensor to alternately receive light that has been transmitted through the cell, and light that has passed through the attenuator. A servomechanism controls the attenuator that is actuated by the output from the sensor and adjusts the light transmission until both beams have the same intensity. The amount of light that is absorbed is indicated by the position of the attenuator. In other words, the amount of light, of a particular wavelength, which is absorbed by the sample, is measured by attenuating the reference beam until its intensity is equivalent to that of the beam transmitted through the sample. The resolution is controlled by the width of the slit, which is adjustable. In the older versions of this type of IR spectrometer, an analogue plotter, mechanically associated with the attenuator, recorded the Spectrum. More modern techniques acquire the signals from the attenuator and grating position by a compute and produce a Spectrum relating absorbance to wavelength (frequency, or wave number).
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.