UV-visible detection

Thus, overall, it is clear that flash photolysis with uv-visible detection is effective in establishing the broad outlines of the photochemistry of a particular metal carbonyl. Intermediates can be identified from their reaction kinetics, and sometimes, with the help of uv-vis data from matrix isolation experiments. Structural information from uv-vis flash photolysis is at best sketchy. Many questions remain unanswered. Time-resolved IR measurements can fill in some of these answers. 

The combination of high-pressure liquid chromatography (HPLC) with monitoring by UV/visible detection provides an accurate, precise and robust method for quantitative analysis of pharmaceutical products and is the industry standard method for this purpose. 

Decomposition of 2,6-difluorophenyl azide by LFP (266 nm) generated a singlet nitrene which was detected by time-resolved IR spectroscopy (1404 cm-1).75 The nitrene could only be detected between 243 and 283 K. At 298 K, the nitrene decay products, a ketenimine (1576 cm-1) and a triplet nitrene (1444 cm-1), were observed. The IR assignments were consistent with DFT calculations and previous UV-visible detection results. 

Early experiments to search for the Cr(CO)s molecnle involved flash photolysis of cyclohexane solutions of Cr(CO)6 with UV-visible detection. Problems arose owing to impurities in the solvent interacting with unsaturated intermediates. Although some evidence was obtained for naked Cr(CO)s it was not possible to confirm the existence of this species nor to distinguish between sqnare pyramidal, C4 (17), and trigonal bipyramidal, D h (18), geometries see Isomer, Types of). 

These findings indicate general difficnlties in interpreting the results of flash photolysis experiments with UV visible detection. First, no detailed structural information can be obtained. Second, minnte traces of imparity in the solvent interfere strongly with the spectral behavior. It has now become clear that Cr(CO)s (and other unsaturated carbonyls) are almost always complexed by solvent or matrix molecnles or atoms. Even in a neon matrix there is some interaction to produce the species Ne- Cr(CO)5. Naked Cr(CO)s can be made in the gas phase, and by some rather cunning time-resolved solution experiments. Here, solvated Cr(CO)s is formed by UV photolysis of Cr(CO)6, then the solvating molecule is removed by visible photolysis. Fast time-resolved spectroscopy allows the decay of the naked Cr(CO)s, as it resolvates, to be moiutored. It is clear that this decay is extremely rapid. 

FIGURE 7.1. The thiocarbamylation reaction of FITC with an amine (where R represents an organic group of a hydrogen) to produce a fluorescent/UV-visible detectable derivative of the amine. 

Before considering some of these complexometric procedures with final UV-visible detection, designed for the simultaneous determination of metallic constituents, a more simple approach must be considered. If some metallic constituents absorb in the UV-visible region, it is interesting to check the feasibility of a direct measurement without reagent. This is studied in the first part with the determination of some chromium ions. 

Bichsel, Y. Von-Gunten, U. (1999). Determination of Iodide and lodate by Ion Chromatography with Postcolumn Reaction and UV/Visible Detection. Anal Chem, Vo. 71, No.l, pp 34-38, ISSN 0003-2700... 

Photolysis at 270 run of diazoacetone with ultrafast IR detection gives ketene generation in a concerted process, interpreted as showing a predominance of the syn-conformation of the diazo ketone (Scheme 7.48). Photolysis of azibenzil with UV-visible detection shows formation of the singlet benzoylcarbene in acetonitrile. The IR absorbance at 2100cm shows formation of the ketene by a concerted process arising from the syn[Pg.250]

Changes in UV-visible absorption maxima (intensity and wavelength) can occur by the addition of surfectants. Several analytical procedures developed in Micellar Liquid Chromatography (MLC) with UV-visible detection were presented in Clmpters 10 and 11. Most procedures were applied to the analysis of phammceutical preparations and physiological fluids. Although it was obvious that several compounds experienced... 

Recent developments have been directed toward the simultaneous determination of multiple vitamins in foods. Separation of vitamins A, E, D2, and D3 in lacteal matrices has been performed using RP-LC with methanohwater as the mobile phase and UV detection at 265 nm (or at the wavelength of maximum absorption of each individual form), after exhaustive saponification. Normal-phase LC has also been used to analyze multiple fat-soluble vitamins in seed oils after extraction or even direct injection of the sample prior to analysis. UV detection has also been used. Sometimes a combination of two detection systems such as UV-visible detection and fluorescence have been used to, for example, determine, respectively, the carotenoids and fat-soluble vitamins in foods. 

Sun, H.-L. Liu, H.-M. Tsai, S.-J. Quantitative analysis of manganese, chromium and molybdenum by ion-pair reversed-phase high-performance liquid chromatography with pre-column derivatization and UV-visible detection. J. Chromatogr. A, 1999, 857, 351-357. 

HPLC coupled with a mass detector has been shown to be suitable for determining minor differences in molecular masses, and thus can satisfactorily replace the UV-Visible detection method. In this destructive detection system, ideal separation (resolution below 1.5) is not required for completing the validation of identification and quantification procedures. However, the HPLC-mass-mass technique is not cost-effective and is more suitable for research centers. However, at present, the HPLC-UV technique is easily affordable in both developed and developing countries. 

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