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.
The sample cells used for fluorometric measurements must be constructed of materials that are transparent to the wavelength of light being measured. Even very pure materials may still have traces of fluorescent contaminants and new or replacement cells should always be examined for background Fluorescence. Cells and other glassware employed in fluorescent measurements should be well cleaned and preferably boiled in 50% nitric acid solution followed by careful rinsing with distilled water. Any solvents employed must be checked for background Fluorescence; if inherent Fluorescence is found present in a solvent it can often be removed by distillation. If water is to be used as the solvent it should be deionized distilled water. Plastic containers should be assiduously avoided as trace florescent materials can be leached from the plastic by any solvents stored in them. High quality solvents should always be used and blank fluorescent measurements taken before use. Although commonly used for cleaning glass apparatus, commercial detergents should be avoided, as some are strongly fluorescent; if detergents are used, then their fluorescent properties should be evaluated prior to use. Fluorescent contaminants can arise from stopcock grease, filter paper and from micro organisms developing over time in buffer solutions. Dilute solutions are basically unstable and should be prepared immediately prior to use from strong standard solutions that may be stored with some confidence over extended periods of time. The surface of glass and other types of containers can absorb substances onto their surface and if the concentration of those substances is very small, adsorption can remove a significant amount of the analyte from solution and impair the accuracy of any measurement. For example glass surfaces have strongly polar interactive sites and if an aromatic hydrocarbon dissolved at very low concentrations in a dispersive solvent (e.g. n-heptane, or petroleum ether ) is stored in a glass bottle, the glass surface will become saturated with adsorbed aromatic hyrdrocarbon. Thus, its concentration in the dispersive solvent will be significantly reduced and any analysis of the solution will give low results. Under certain circumstances the intensity of the excitation light can cause analyte decomposition. This effect can be reduced employing an appropriate shutter between the light source and the sample cell and this shutter is only opened for a short time during measurement. Better alternatives are to identify a wavelength for the excitation light that does not cause sample decomposition or reduce the excitation light intensity by using a narrower slit. Finally, the presence of oxidising agents (e.g. dissolved oxygen or the presence of peroxides ) may initiate a reaction with the Fluorescence substance and consequently reduce the Fluorescence. Care must be taken to ensure such oxidising agents are absent from the sample.
A typical example of a Fluorescence spectrometer is that manufactured by SHIMADZU for routine research and routine analytical purposes and is shown in figure 11. The compact, high sensitivity model of this range can handle extremely small samples and easily detect and determine trace concentrations of pollutants. Capillary cells having volumes of 5 μl or less are also available.
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.