Ultraviolet/visible spectrophotometry applications

Following ultraviolet-visible spectrophotometry and infrared (IR) spectroscopy, gas chromatography (GC) was one of the first instrumental techniques to help in solving forensic science problems. The early very successful applications included the determination of blood alcohol by direct injection of blood or serum, and the detection and identification of petroleum products in debris from arson cases in 1958/59. The breakthrough of GC in these areas and in drug analysis was an event of the 1960s and the 1970s. 

The selective absorption of ultraviolet, visible and infrared radiation by molecules is explained in a descriptive manner that stresses how the noncontinuous energy requirements of chemical substances can only be satisfied by photons that have energy values equivalent to that of the differences in energy levels of the molecule in question. The meaning and quantitative significance of Beer s Law is briefly discussed. The components of a simple spectrophotometer are illustrated, accompanied by a demonstration of the operation of a spectrophotometer in the laboratory. Actual applications of the techniques of spectrophotometry are described during the presentation of relevent topics, for example, in drug identification. 

Frequently industrial hygiene analyses require the identification of unknown sample components. One of the most widely employed methods for this purpose is coupled gas chromatography/ mass spectrometry (GC/MS). With respect to interface with mass spectrometry, HPLC presently suffers a disadvantage in comparison to GC because instrumentation for routine application of HPLC/MS techniques is not available in many analytical chemistry laboratories (3). It is, however, anticipated that HPLC/MS systems will be more readily available in the future ( 5, 6, 1, 8). HPLC will then become an even more powerful analytical tool for use in occupational health chemistry. It is also important to note that conventional HPLC is presently adaptable to effective compound identification procedures other than direct mass spectrometry interface. These include relatively simple procedures for the recovery of sample components from column eluate as well as stop-flow techniques. Following recovery, a separated sample component may be subjected to, for example, direct probe mass spectrometry infra-red (IR), ultraviolet (UV), and visible spectrophotometry and fluorescence spectroscopy. The stopped flow technique may be used to obtain a fluorescence or a UV absorbance spectrum of a particular component as it elutes from the column. Such spectra can frequently be used to determine specific properties of the component for assistance in compound identification (9). 

Ultraviolet spectrophotometers cont.), single-beam, 225 standardisation, 226 Ultraviolet spectrophotometry, 221-232 absorption cells, 226 colorimetry, 228 derivative, 230 difference method, 229 dual-wavelength, 229 identification by, 231 influence of pH, 224 influence of solvent, 224 laws of absorption, 222 quantitative applications, 227 stray-light effects, 224 Ultraviolet-visible detector, 202 multiwavelength, 211 Unicontin, 1011 Unidiarea, 474 Unidone, 356 Uniflu, 557, 893 Unilobin, 709 Unimycin, 846 Uniphyllin, 1011 Uniprofen, 677 Unisom, 576... 

Upstone SL. Ultraviolet/visible light absorption spectrophotometry in clinical chemistry. In Meyers RA, ed. Encyclopedia of analytical chemistry Applications, theory, and instrumentation. New York John Wiley Sons, 2000 1699-713. 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

Sanchez Rojas F, Bosch Ojeda C, and Cano Pavon JM (1988) Derivative ultraviolet-visible region absorption spectrophotometry and its analytical applications. Tal-anta 35 753-761. 

The applications of quantitative, ultraviolet-visible absorption methods not only are numerous but also touch on every field that requires quantitative chemical information. The reader can obtain a notion of the scope of spectrophotometry by consulting the scries of review articles that were published in Analytical Chemistry S as well as monographs on the subject."... 

Analytical Applications of Ultraviolet, Visible, and Near-Infrared Absorption Spectrophotometry by Robert G. White 237... 

Absorption spectrophotometry in the ultraviolet, visible, and near-infrared spectral regions has become an extremely important analytical tool in the last two decades, its progress having been greatly accelerated by the development of commercially available recording spectrophotometers. This paper briefly discusses its history, describes laboratory techniques, and cites many practical applications from the chemical literature. It is intended both to introduce the novice to the field and to acquaint the specialist with the versatility of these techniques. 

Quantitative analysis in the infrared region is based on considerations similar to those applied routinely in visible and ultraviolet spectrophotometry, namely, application of the Beer-Lambert law. The law states that at a given wavelength of light... 

Spectrophotometry in the ultraviolet (UV) range has repeatedly proven to be a fast, inexpensive and reliable method for the monitoring of many compounds in urban and industrial wastewaters (Narayana and Sunil 2009 Pinheiro et al. 2004). Through the application of spectral analysis, quantitative and qualitative wastewater parameters can be estimated on direct samples in just a few minutes, using portable or online field instrumentation. Perez (2001) has successfully applied UV spectral deconvolution on wastewater monitoring in a chemical industry, for the estimation of aniline derivative concentrations. In the case of textile effluents, the use of the UV range of the spectra (200-350 nm) for aromatic amine determination is particularly useful to avoid interference by visible colour of dyes. The characteristic... 

Relatively few analogous applications have been published for the visible and ultraviolet regions. One good example is Beroza s paper on differential multicomponent ultraviolet spectrophotometry applied to mixtures of benzyl benzoate and n-butyl acetanilide. Other applications are discussed under pH effects. 

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