Ultraviolet/visible spectrometry

Ultraviolet/visible spectrometry Miscellaneous conventional techniques and neutron activation analysis... 

Table 16-1 gives the rough limits of each of the three regions. Measurements in the near-lR region are often made with photometers and spectrophotometers similar in design and components to the instruments described in earlier chapters for ultraviolet-visible spectrometry. The most important applications of this spectral region have been to the quantitative analvsis of industrial and agricultural materials and for process control. Applications of near-IR spectrometry are discussed in Section 17D. 

PTM- in solution is also light-sensitive (Ballester, 1967), its disappearance having been monitored by ultraviolet/visible spectrometry. Under the suspicion that perchloro-9-phenylfluorenyl radical (PPF-) is formed, the illumination was performed in carbon tetrachloride in the presence of CI2 as a radical scavenger, and accordingly some perchloro-9-phenylfluorene was obtained, among other chlorocarbons (171) (Badia, 1969). The esr signal... 

When feasible, a convenient way of obtaining IR spectra is on solutions prepared to contain a known concentration of sample, as is generally done in ultraviolet-visible spectrometry. This technique is somewhat... 

Ultraviolet/visible spectrometry Electronic molecular absorption in solution Quantitative determination of unsaturated organic compounds... 

Non-dispersive analysers are occasionally useful, for example in gas analysis by infrared and ultraviolet-visible spectrometry. 

Key abbreviation (in alphabetical order) AAS atomic absorption spectrometry ECD electron capture detector FID flame ionization detector GC gas chromatography LC liquid chromatography TLC in layer chromatography UVA ultraviolet/visible spectrometry. Symbol means coupling between techniques. 

A method based on ultraviolet/visible spectrometry (UVA IS) is proposed for the determination of oxyquinoline and its sulphate. On the other hand, liquid chromatography (LC) with UVA IS detector is used for the determination of quinine and its salts. 

Ultraviolet visible (UV VIS) spectroscopy, which probes the electron distribution especially m molecules that have conjugated n electron systems Mass spectrometry (MS), which gives the molecular weight and formula both of the molecule itself and various structural units within it... 

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. 

Measurement techniques that can be employed for the determination of trace metals include atomic absorption spectrometry, anodic stripping voltammetry, differential pulse cathodic stripping voltammetry, inductively coupled plasma atomic emission spectrometry, liquid chromatography of the metal chelates with ultraviolet-visible absorption and, more recently, inductively coupled plasma mass spectrometry. 

Table 9.1 Components of instruments used for ultraviolet, visible, infrared and magnetic resonance spectrometry. 

PMR spectrometry is an extremely useful technique for the identification and structural analysis of organic compounds in solution, especially when used in conjunction with infrared, ultraviolet, visible and mass spectrometry. Interpretation of PMR spectra is accomplished by comparison with reference spectra and reference to chemical shift tables. In contrast to infrared spectra, it is usually possible to identify all the peaks in a PMR spectrum, although the complete identification of an unknown compound is often not possible without other data. Some examples of PMR spectra are discussed below. 

Green L.R. and Hart F.A. (1987). Colour and chemical composition of ancient glass an examination of some Roman and Wealden glass by means of ultraviolet-visible-infra-red spectrometry and electron microprobe analysis. Journal of Archaeological Science 14 271-282. 

Chromatographic methods are also often used as part of systems that are called hyphenated methods, (see Chapter 15) where the output of the chromatographic section is used as the input for an identification method such as mass spectrometry. These hyphenated methods are also most often referred to by their acronyms, for example, GC-MS—gas chromatography-mass spectrometry and HPLC-MS—high-performance liquid chromatography-mass spectrometry. Note that although ultraviolet-visible (UV-Vis) is hyphenated, it is not a hyphenated method in that it does not consist of two different methods of analysis. Hyphenated methods will be discussed fully in Chapter 15. 

CE is based on the use of narrow-bore capillaries with internal diameters typically betwen 20 and 150 pm. Because most commercial instruments equipped with ultraviolet/visible (UV-Vis) absorption detectors use a segment of the same capillary as the detection cell, the path length in CE is much less compared to those in HPLC or spectrometry. Therefore, the most commonly used CE detectors... 

After s)mthesis it is important to determine the drug s exact chemical structure. This will involve a variety of techniques such as mass spectrometry, nuclear magnetic resonance (H and C ), infrared and ultraviolet/visible spectrophotometry along with elemental analysis. This will confirm the medicinal chemist s proposed... 

To bring you up to speed on spectroscopy, we cover the basics in Chapter 5. We give you the executive summary on infrared (IR), ultraviolet-visible (UV-vis), mass spectrometry (mass spec), and nuclear me netic resonance (NMR). In addition, many of the chapters in this book have a spectroscopy section at the end where we simply cover the essentials concerning the specific compounds that you study in that chapter. 

We will concentrate upon the most commonly used techniques in organic structure determination nuclear magnetic resonance (NMR), infrared (IR) and ultraviolet-visible (UV-Vis) spectroscopy, and mass spectrometry (MS). The amount of space devoted to each technique in this text is meant to be representative of their current usage for structure determination. 

The system relies upon preliminary fractionation of the microbial crude extract by dualmode countercurrent chromatography coupled with photodiode array detection (PDA). The ultraviolet-visible (UV-Vis) spectra and liquid chromatography-mass spectrometry (LC-MS) of biologically active peaks are used for identification. Confirmation of compound identity is accomplished by nuclear magnetic resonance (NMR). Use of an integrated system countercurrent chromatography (CCC) separation, PDA detection, and LC-MS rapidly provided profiles and structural information extremely useful for metabolite identification (dereplication, Figure 14.1). 

The techniques considered in this chapter are infrared spectroscopy (or vibrational spectroscopy), nuclear magnetic resonance spectroscopy, ultraviolet-visible spectroscopy (or electronic spectroscopy) and mass spectrometry. Absorption of infrared radiation is associated with the energy differences between vibrational states of molecules nuclear magnetic resonance absorption is associated with changes in the orientation of atomic nuclei in an applied magnetic field absorption of ultraviolet and visible radiation is associated with changes in the energy states of the valence electrons of molecules and mass spectrometry is concerned... 

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