UV/VIS spectrophotometers

Measurements were performed employing a Perkin Elmer X2, 5 or 12 UV-Vis spectrophotometer at 25 O.r- C. Equilibrium constants were determined by measuring the extinction coefficient at a suitable wavelength of the partially complexed dienophile (y,.hs) as a function of the concentration of... 

Finally, values of sx are directly proportional to transmittance for indeterminate errors due to fluctuations in source intensity and for uncertainty in positioning the sample cell within the spectrometer. The latter is of particular importance since the optical properties of any sample cell are not uniform. As a result, repositioning the sample cell may lead to a change in the intensity of transmitted radiation. As shown by curve C in Figure 10.35, the effect of this source of indeterminate error is only important at low absorbances. This source of indeterminate errors is usually the limiting factor for high-quality UV/Vis spectrophotometers when the absorbance is relatively small. 

Kinetic measurements were performed on a Hitachi 150-20 UV/VIS spectrophotometer. Dehydrobrominations were studied in DMF solution using cyclohexyl amine (CHA) as the base. Applied CHA concentrations were 2, 2.5, 3, 3.5, 4 and 5 10 3 mole.dm-3, initial concentration of 1 was 5 10 5 mole.dm-3 in every case (pseudo-first-order conditions). Ionic strength was adjusted to lO l mole.dm 3 with potassium nitrate. Kinetic curves / D(t) / were recorded at fix wavelength, X = 290 ran and the temperature was maintained at 30, 35.5, 40°C. Stock solutions were made daily for la and freshly for every measurement of Ih. The reaction was started by injection of solution of 1 to the thermostated solution of CHA. 

Conventional UV/VIS spectrophotometer (manual measurements from strip-chart recorder traces and calculations on the basis of fitted polynomials the extraction/separation step remains). 

The formation of monomer and dimer of (salen)Co AIX3 complex can be confirmed by Al NMR. Monomer complex la show Al NMR chemical shift on 5=43.1 ppm line width =30.2 Hz and dimer complex lb 5=37.7 ppm line width =12.7 Hz. Further instrumental evidence may be viewed by UV-Vis spectrophotometer. The new synthesized complex showed absorption band at 370 nm. The characteristic absorption band of the precatalyst Co(salen) at 420 nm disappeared (Figure 1). It has long been known that oxygen atoms of the metal complexes of the SchifT bases are able to coordinate to the transition and group 13 metals to form bi- and trinuclear complex [9]. On these proofs the possible structure is shown in Scheme 1. 

The general operation of the pilot scale reactor has be previously described by Pareek et. al. [3]. However, modifications were required to allow the injection of the gas and liquid tracers, and their subsequent detection at the outlets. The liquid tracer, 5mL Methyl blue solution (lOgL" ), was injected via a syringe inserted into the liquid feed line. Outlet samples were measured with a Shimadzu 1601 UV-Vis Spectrophotometer at a wavelength of 635nm. A pulse (20mL) of helium gas tracer was introduced using an automated control system, with the outlet concentration monitored in real-time with a thermal conductivity detector. Runs were carried out based on a two-level... 

Spectroscopic evaluation of the catalysts. The UV-Vis spectra of the Jacobsen Co-salen catalysts were collected in the transmission mode on a CARY-3E UV-Vis spectrophotometer by dissolving the catalysts in epichlorohydria The Co K-edge (7709 eV) X-ray absorption near edge stracture, XANES, of Jacobsen s Co-salen catalyst was collected during the HKR reaction at beamline XIO-C at National Synchrotron Light Source (NSLS), Brookhaven National Lab, Upton, NY. 

Concentration-sensitive detectors, such as the refractive index detector or UV-VIS spectrophotometer... 

Methodology The ultrasonic probe is used for the experiment which allows relatively more acoustic energy directly into the system. Indicators were sonicated for different durations and the absorbance was recorded using UV-vis spectrophotometer. The values, however, given in the table below give qualitative idea of the degradation of indicators. 

The UV absorption spectra of niclosamide in methanol, methanolic 0.1 N HC1 and methanolic 0.1 N NaOH are shown in Fig. 3. The figures were recorded using a Perkin-Elmer double beam model 550s UV-Vis spectrophotometer. The values of the log emax (log molar extinction coefficient) at their corresponding wavelength maximum in nanometers (2max) are shown in the following table. 

Many compounds have large molar absorptivities,1 and thus only small amounts are needed to obtain a spectrum. Most UV-Vis spectrophotometers give the most accurate absorbance values when the absorbance measurements are between 0 and 1 absorbance unit. Often, a sample will have an absorbance... 

Photomultiplier tubes or photodiodes (light sensors) are used as detectors in UV-VIS spectrophotometers, while thermcouples (heat sensors) are used as detectors for infrared (IR) spectrometry. This is the reason UV-VIS instruments are called spectrophotometers while IR instrument are called spectrometers. 

Obtain an absorption spectrum of each of your standards, the unknown, and the control sample on a scanning UV-VIS spectrophotometer interfaced to a computer for data acquisition. Follow the instructions provided for your instrument and software. 

Even with the knowledge of the reactive moieties that are suspected to trigger M BI, there are numerous potential pathways for the chemistry to lead to protein inactivation [174,196]. Differentiating these mechanisms can facilitate the generation of alternate and safer chemical scaffolds. The UV-Vis spectrophotometer has been a key instrument in activity and functional characterization for CYPs for the past 40 years, as indicated by the derivation of its name, pigment 45 0 being the signature UV band present when reduced in the presence of CO [5,197]. This technique has been... 

The above two modifications have been duly incorporated in a double-beam spectrophotometer. Figure 21.6, depicts the schematic diagram of the optical system involved in a Lambda-2 microcomputer-controlled UV-VIS Spectrophotometer (Perkin-Elmer). 

The absorbance measurements were performed with an Agilent 8453 UV-Vis Spectrophotometer, using 1,00 cm quartz cells, PLS-1 was applied with an in-house program written according to the algorithm given by Martens and Naes [23],... 

The absorbance measirrements were performed with an Agillant 8453 UV-Vis Spectrophotometer using 1.00 qitartz cells. Computations were run on Pentiirm-100 computer. A computer program for PLS-2 was written according to the algorithm... 

UV-vis spectrophotometer Merck 60 F254 TLC plates rotary evaporator... 

Apparatus. Infrared spectroscopy, Perkin-Elmer Model 257 infrared spectrophometer, Perkin-Elmer Corporation (Norwalk, CT) ultraviolet spectroscopy, Perkin-Elmer Model 559 UV-vis spectrophotometer, Perkin-Elmer Corporation, Coleman... 

The emergence of sensitive and affordable array detectors in 1980s and 1990s has also improved measurement capability in the UV-vis. Commercially available UV-vis instrumentation with photodiode-array (PDA) detectors appeared in the mid-1980s. This made it possible to produce a UV-vis spectrophotometer... 

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