Visible ultraviolet infrared coupling

Ultraviolet, visible, and infrared spectroscopies refer to analysis of the absorption characteristics of a sample that are linked to various electronic and vibrational transitions within a molecule [17]. These involve relative displacements of electrons and nuclei that are able to couple to incident light if they induce a dipole in the material. The strength of this coupling is measured by the transition dipole moment [17],... 

Analytical techniques used in qualitative analysis include flame tests (Chapter 2) and precipitation reactions (Chapters 3 and 13). Analytical techniques used in quantitative analysis include titrations (Chapter 1), inductively coupled plasma (ICP) spectroscopy (Chapter 22 on the accompanying website), ultraviolet—visible spectroscopy (Chapter 23 on the accompanying website), infrared spectroscopy and various chromatographic techniques (Chapter 23). Analytical techniques used in structural analysis include NMR, IR spectroscopy, mass spectrometry and visible—ultraviolet spectroscopy. Important areas that employ analytical techniques include ... 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

A photomultiplier tube is a sensitive detector of visible and ultraviolet radiation photons cause electrons to be ejected from a metallic cathode. The signal is amplified at each successive dynode on which the photoelectrons impinge. Photodiode arrays and charge coupled devices are solid-state detectors in which photons create electrons and holes in semiconductor materials. Coupled to a polychromator, these devices can record all wavelengths of a spectrum simultaneously, with resolution limited by the number and spacing of detector elements. Common infrared detectors include thermocouples, ferroelectric materials, and photoconductive and photovoltaic devices. 

Coupled spectroscopic methods such as TLC-UV (ultraviolet) and visible spectroscopy, TLC-mass spectrometry, and TLC-FTIR (Fourier transform infrared) have been developed to overcome this difficulty [7]. Their future application in the TLC analysis of natural pigments will markedly increase the information content of this simple and interesting separation technique. The automation of the various steps of TLC analysis (sample application, automated developing chambers, TLC scanners, etc.) greatly increased the reliability of the method, making it suitable for official control and legislative purposes [8]. 

Table 21.1 classifies popular LC detectors according to several criteria for purposes of comparison. At the present time, LC detectors are generally less sensitive than GC detectors, which can detect picograms of material under good conditions. Most LC detectors provide only limited structural information. However, spectrophotometers fitted with micro flow-cells can be used to obtain a stop-flow ultraviolet-or visible-absorption spectrum of an LC peak trapped in the flow cell. On-line coupling of liquid chromatographs with mass or infrared spectrometers offers sophisticated, but indeed expensive, detection/identification methods. Such systems have been described in the literature, but are quite limited by the solvents that can be used in the chromatography step. 

Unlike IR spectroscopy where nowadays FT instrumentation is solely used, in Raman spectroscopy both conventional dispersive and FT techniques have their applications, the choice being governed by several factors. The two techniques differ significantly in several performance criteria, and neither one is best for all applications. Contemporary dispersive Raman spectrometers are often equipped with silicon-based charge coupled device (CCD) multichannel detector systems, and laser sources with operating wavelength in the ultraviolet, visible or near-infrared region are employed. In FT Raman spectroscopy, the excitation is provided exclusively by near-infrared lasers (1064 nm or 780 nm). 

Fourier transform infrared spectrophotometry (FTIR) spectra of the neutral pol5mier PEDOT indicates a regular structure formed via a-a coupling of thiophene rings. The polymer shows two absorption bands at 341 nm and 413-419 nm in an N-methyl-2-p5n-rolidone (NMP) solution in the ultraviolet-visible (UV-Vis) luminescence with peak at ca. 552 nm. 

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. 

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