UV-vis. spectroscopic measurements

For measurements at temperatures other than ambient, cells with double walls, which can be thermostatted, are also available commercially. If measurements are required at temperatures between ca. —5°C and room temperature, the sample compartment of the spectrometer can be flushed with dry air or nitrogen to reduce condensation on the cell windows. Below ca. — 5 °C the windows can be covered with a thin polythene film, but measurements below —25 °C are very troublesome. The problems associated with low temperature spectroscopic measurements were solved by enclosing the cell in an air-tight box fitted with glass windows (Dadley and Evans, 1967). The box was so designed that it fitted into the spectrophotometer and the air inside the box was dried with phosphoric oxide which, it is claimed, stopped condensation even at temperatures as low as — 60 °C glass windows could be used because only absorptions above 380 nm were of interest. 

Recent developments in fibre optics have made it possible to measure the spectrum in any kind of vessel, including any which form part of a vacuum apparatus, so that the problem of fitting a cell which is part of a vacuum rig into a spectrophotometer is now effectively obsolete. However, for single or occasional measurements the devices discussed here are simpler and very much cheaper than fibre-optic gadgetry. 

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Endo et al. [96] prepared AuPt, AuPd, and PtPd bimetallic nanoparticles with 2 nm in particle size in order to investigate catalytic activity for reduction of p-nitrophenol in water. The binary features of the nanoparticles were characterized by UV-Vis spectroscopic measurements. 

Most liquid- and gas-phase UV-vis spectroscopic measurements rely on the well-known Lambert-Beer Law ... 

In case of ions, it is important to know the coordination environment to extract metals. UV-Vis spectroscopic measurements provide the respective information. There are systems in which both the biphasic extraction equilibrium and the metal coordination environment in an IL and a molecular organic solvent are the same [17]. 

N, adsorption for determination of pore size distribution(BJH method) using a Micrometries ASAP 2000 automatic analyzer. FTIR spectra were recorded on a PerkinElmer 221 spectrometer and UV-vis spectroscopic measurments were carried out using Varian CARY 3E double beam spectrometer in the range of 190 - 820 nm. 

Most liquid- and gas-phase UV-vis spectroscopic measurements rely on the well-known Beer s Law1 (Equation 6.1) to relate the amount of light absorbed by a sample to the quantity of some chemical species that is present in that sample. 

Weckhuysen and coworkers (Nijhuis et al., 2003) described equipment suitable for parallel Raman and UV-vis spectroscopic measurements. Openings on the opposite sides of a furnace allowed acquisition of Raman and UV-vis spectra through optical grade windows in a tubular quartz reactor. UV-vis spectra were recorded at 823 K. Gas-phase analysis was achieved with mass spectrometry and gas chromatography. A more advanced version of the design (Nijhuis et al., 2004) accommodates four optical fiber probes, placed at 10-mm vertical spacing along the tubular reactor. The temperature that the fibers can withstand is 973 K the reported spectra characterize samples at 823 K. 

In Table 2, an overview of UV-vis spectroscopic measurements conducted during treatments is given. Novel experimental designs and observations of general importance are highlighted below. 

The primary standard betaine dye (44) is only sparingly soluble in water and less polar solvents it is insoluble in nonpolar solvents such as aliphatic hydrocarbons. In order to overcome the solubility problems in nonpolar solvents, the more lipophilic penta-t-butyl-substituted betaine dye (45) has additionally been used as a secondary reference probe [174]. The excellent Hnear correlation between the Ej values of the two dyes allows the calculation of t(30) values for solvents in which the solvatochromic indicator dye (44) is not soluble. Introduction of electron-withdrawing substituents e.g. Cl [323], F, CF3, C6F13 [324]) in the betaine molecule reduces the basicity of its phenolate moiety, which allows the direct determination of x(30) values for somewhat more acidic solvents. Moreover, the Hpophilic and fluorophilic penta(trifluoromethyl)-substituted betaine dye (46) is more soluble in nonpolar solvents e.g. hexafluoro-benzene) than the standard dye (44) [324]. Conversely, the solubility in aqueous media can be improved through replacement of some of the peripheral hydrophobic phenyl groups in (44) by more hydrophilic pyridyl groups, to yield the more water-soluble betaine dye (47) [325]. The Ej values of these new secondary standard betaine dyes correlate linearly with the x(30) values of (44), which allows the calculation of x(30) values for solvents in which only betaine dyes (45)-(47) are sufficiently stable and soluble for the UV/Vis spectroscopic measurements [324, 325]. 

The in situ UV-VIS spectroscopic measurement showed that upon adsorption of propene/benzene=l/6 mixture on HP at 295 K, bands at 210, 260 and 340 nm appeared (Fig. 8), whose intensities did change neither -with time nor upon evacuation at room temperature. When evacuation was performed at 373 K the band at 340 nm increased gradually, while at 473 K new bands appeared at 400-500 nm indicating the surface transformation became more complex. 

A similar result was obtained for porphyrin derivatives. UV-vis spectroscopic measurements reveal a red shift and broadening of Soret and Q bands in LB films... 

When the water content further increases, the isomerization degree starts to decrease. When the water content increases from 37.5% to 80% (vol%), the isomerization degree decreases from 80% to ca. 55%. For the spheres in the water suspension, obtained by quenching with an excessive amount of water and dialysis, the isomerization degree decreases to even 33%. The preceding results obtained from the UV-vis spectroscopic measurements indicate that in the water addition process, the aggregates undergo a collapse process after the water content is above 40% (vol%). 

There is little to no preparation time involved in a UV-Vis spectroscopic measurement. The amount of time required to conduct the experiment is minimal and mostly determined by the time required for the lamp to warm up. Sampling time itself will vary depending on the speed and range of the scan but generally takes no more than a few minutes. Analysis time is similarly expedient, requiring no more than a few minutes to plot the data in a spreadsheet program. 

In the CTAB-hexanol-water microemulsion system, the Ni(II) and Co(II) ions are not dispersed in the water core they are located in an envelope in the vicinity of the interface as was shown by and UV-Vis spectroscopic measurements. The Ni(II) local concentration is more important than the global concentration, with a correction factor given by [3]... 

Comparison of the sensitivity of PA and UV-VIS spectroscopic measurements, (a) PA and UV-VIS signal responses at pre- and post-aggregation optical responses, as a function of increasing concentrations of AuNPs and GSH. (b) Comparison of the quantitative responses obtained from both spectroscopic methods at 620 nm for the respective concentrations of AuNPs (lower x-axis) and GSH (uppery-axis). 

The first in situ cell for simultaneous ATR-FTIR/UV-vis spectroscopic measurements was described by Biirgi [10]. Further developments were published by the Baiker group [29] and by the Lefferts group [41]. By replacing the cover of the flow-through cell by a quartz window (Figure 3.6), the monitoring of photocatalytic reactions becomes possible (e.g., [42-44]). 

An amperometric biosensor for trans-resveratrol determination in aqueous solutions by means of carbon paste electrodes modified with peroxidase basic isoenzymes (PBIs) from Brassica napus was developed [182]. Catalytic properties of PBIs from Brassica napus toward trows-resveratrol oxidation were demonstrated by conventional UV-vis spectroscopic measurements. The enzymatic reaction rate was studied and kinetics parameters were detected. An amperometric biosensor based on Brassica... 

The characterization of different biofunctionalities attached to the backbone of oligomers and polymers is normally carried out by cyclic voltammetric and UV-Vis spectroscopic measurements. Additionally,... 

The band gap and band edge positions of saniconductors are the most critical parameters for assessing the suitability of photocatalysts for overall water spUtting. The absorption properties can be evaluated from UV-Vis spectroscopic measurements in... 

M Carrott, CM Wai. UV-Vis spectroscopic measurement of solubilities in supercritical CO2 using high pressure fiber optic cells. Anal Chem 70 2421-2425, 1998. Mike J. Carrott, Brenda E. Waller, Neil G. Smart, Chien M. Wai, High solubility of U02(N03)2 2TBP complex in supercritical CO2. Chem Commun 373-374, 1998. CM. Wai, B Waller. Dissolution of metal species in supercritical fluids—principles and applications. Ind Eng Chem Res 39 3837-3841, 2000. 

Excluding the incorrect use of the instrumentation or its malfunctioning, the most common errors in UV-vis spectroscopic measurements are due to the composition and/or to the treatment of the sample. 

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