UV-visible region

Hydantoin derivatives show weak absorption in the uv-visible region, unless a part of the molecule other than the imidazohdinedione ring behaves as a chromophore (13) however, piC values have been determined by spectrophotometry in favorable cases (14). Absorption of uvby thiohydantoins is more intense, and the two bands observed have been attributed to n — tt and n — tr transitions of the thiocarbonyl group (15,16). Several piC values of thiohydantoins have been determined by uv-visible spectrophotometry (16). 

The ionic or polar substances can be seperated without any reaction on specially treated chromatographic columns and detected refractometrically. This is necessary because alkyl sulfosuccinates show only small absorption in the UV-visible region no sensitive photometric detection can be obtained. Separation problems can arise when common steel columns filled with reverse phase material (or sometimes silica gel) are used. This problem can be solved by adding a suitable counterion (e.g., tetrabutylammonium) to the mobile phase ( ion pair chromatography ). This way it is possible to get good separation performance. For an explanation of separation mechanism see Ref. 65-67. A broad review of the whole method and its possibilities in use is given in an excellent monograph [68]. 

This chapter focuses on recent developments in the design and applications of fluorescent organic markers, such as coumarins, benzoxadiazoles, acridones, acridines, polyaromatics (naphthalene, anthracene, and pyrene), fluorescein, and rho-damine derivatives, which display maximum fluorescence emission in the UV/ visible region and have been applied in the labeling of relevant biomolecules, namely DNA, RNA, proteins, peptides, and amino acids, among others. 

As was mentioned, there is an enormous variety of fluorophores with fluorescence emission in the UV/visible region associated with a wide range of applications related to life sciences. These compounds possess a diversity of heteroaromatic or... 

The principle of ICP-AES is that atoms (or sometimes ions) are thermally excited, in a plasma torch, to higher energy levels, these atoms or ions then relax back to lower electronic energy levels by emitting radiation in the UV-visible region. The emitted radiation is detected and used to determine which elements are present, and their concentration. Analysis of organometallic and inorganic additives, based on the ICP-AES determination of specific metal ions, is routinely undertaken. 

Many chemical species exhibit different redox states with distinct electronic absorption spectra, usually in the UV/visible region of the electromagnetic spectrum. Where the switching of redox... 

Spectroelectrochemical cells for use in the UV-visible region are not, of course, constrained by solvent absorption and can thus be of a reasonable size to give acceptable electrochemical behaviour. However, as with all the in situ techniques discussed in this book, a thin-layer approach is one of the methods employed. 

The absorption of electromagnetic radiation by molecular species in solution in the UV/visible region is followed by relaxation from excited electronic states to the ground state mostly by a combination of radiationless processes. Vibrational relaxation, where the excess energy is rapidly dis-... 

As with all other types of spectrometers operating in the UV/visible region of the spectrum, it is advantageous to modulate the primary beam using a mechanical beam chopper, and detect it at the same frequency, to reduce background noise. This is usually done with a rotating beam chopper, shaped... 

The most popular current techniques for amino acid analysis rely on liquid chromatography and there are two basic analytical methods. The first is based on ion-exchange chromatography with post-column derivatization. The second uses pre-column derivatization followed by reversed-phase HPLC. Derivatization is necessary because amino acids, with very few exceptions, do not absorb in the UV-visible region, nor do they possess natural fluorescence. 

Conjugated systems also give characteristic spectral absorptions, especially in the UV-visible regions. As the extent of conjugation increases, i.e. more than two double bonds separated by single... 

Factors governing absorption of radiation in the UV/visible region... 

Figure 11.1—Three different aspects of spectra obtained in the UV/ Visible region, a) Band spectrum of a compound in solution (most frequent case) b) spectrum showing fine structure c) line spectrum obtained with a high resolution instrument. Only 0.14 nm separates the two sides of this spectrum. Absorbance can be measured with up to 6 units of certainty with some instruments, however, high values are not as reliable.

Acetylene Polymers Homopolymers of optically active acetylenes, including (/ )-153 synthesized by [RhCl(norbomadiene)]2 catalyst, show intense CD bands in the UV-visible region, probably based on a predominant helical sense of the main chain [204]. Excess single-handed helicity of the main chain can be induced for polymers of achiral acetylenes (154 and 155) by adding chiral molecules. The chiral induction is based on acid-base interaction or complex formation between the polymer and the additives [205-2081. 

The detection technique which perhaps has the most potential for trace analysis is post-column derivatization. This is based on the formation of reaction products immediately after column elution and prior to detection. The advantage of such a system is that the samples can be chromatographed directly without the need for prior reaction. Post-column reactions can be very selective, permitting only certain solutes to form derivatives for analysis. These derivatives usually absorb strongly in the UV-visible region or they fluoresce. 

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