Spectrophotometers typical

Holmium oxide solution is commercially available in a sealed 1-cm cuvette. It is a very convenient and versatile wavelength standard. The standard is suitable for UV-Vis spectrophotometers typically used in pharmaceutical laboratories, with spectral bandwidth ranging from 2 to 0.5 nm. The certified wavelength values of the peaks are listed in Table 10.3. When a spectral bandwidth of... 

Infrared Spectrometers. Infrared spectroscopy is one of the most powerful tools for quantitative and qualitative identification of molecules, and this led to the early development of prism and grating spectrophotometers. Typically, these instruments cover the region from 400 to 4000 cm, give a resolution of 1 to 4 cm, and require calibration with polystyrene films or with standard gases such as H2O, CO2, CH4, or This al-... 

The most commonly used laboratoiy instrument for the precise measurement of the reflected light (color) is the spectrophotometer. Typically, this instrument is used to record a visible wavelength (400-700 nm) reflectance spectrum which acts as a fingerprint of the colored sample being characterized. The shape of the spectral curve is influenced by the number and types of colorants employed in the sample, the nature of the illuminating light source and the spectral sensitivity of the detector (observer) system. 

The NIR signal is delivered to the sample, which selectively absorbs and reflects or transmits the remainder to the detector. Several different detector types are available for FT-NIR spectrophotometers with advantages and disadvantages (see Table 5.1). Because FT-NIR spectrophotometers typically scan rapidly, detectors that can respond quickly are used. 

In direct dyebath monitoring systems, a small amount of the dyebath circulates through one or more flow cells, where the dyebath absorbance spectrum is measured by a spectrophotometer. The reason for using more than one flow cell is that large variations in the dye concentration will cause absorbances to be measured that are outside the range of the spectrophotometer. Typically, a spectrophotometer operates in a range of 0.005 to 1.5 absorbance units. One of the... 

Kinetic measurements were performed employii UV-vis spectroscopy (Perkin Elmer "K2, X5 or 12 spectrophotometer) using quartz cuvettes of 1 cm pathlength at 25 0.1 C. Second-order rate constants of the reaction of methyl vinyl ketone (4.8) with cyclopentadiene (4.6) were determined from the pseudo-first-order rate constants obtained by followirg the absorption of 4.6 at 253-260 nm in the presence of an excess of 4.8. Typical concentrations were [4.8] = 18 mM and [4.6] = 0.1 mM. In order to ensure rapid dissolution of 4.6, this compound was added from a stock solution of 5.0 )j1 in 2.00 g of 1-propanol. In order to prevent evaporation of the extremely volatile 4.6, the cuvettes were filled almost completely and sealed carefully. The water used for the experiments with MeReOj was degassed by purging with argon for 0.5 hours prior to the measurements. All rate constants were reproducible to within 3%. 

Block diagram for a single-beam fixed-wavelength spectrophotometer with photo of a typical instrument. 

Typical recording spectrophotometers for the near-infrared, mid-infrared, visible and near-ultraviolet regions... 

Figure 3.23 A typical double-beam recording mid-infrared and near-infrared spectrophotometer...

In the case of 2- and 6-hydroxypteridine and their derivatives, the anhydrous species in neutral solutions (produced by rapid addition of equilibrated alkaline solutions to neutral buffers) change sufficiently slowly into the hydrated species that serial scans on a recording spectrophotometer can be used to demonstrate the process. The results shown in Fig. 1 for 6-hydroxy-2-methylpteridine are typical. 

Figure 2.4. Graph of the linear regression line and data points (left), and the residuals (right). The fifty-fold magnification of the right panel is indicated the digital resolution 1 mAU of a typical UV-spectrophotometer is illustrated by the steps.

Pectolytic activity was also studied in batch reactors, following the reaction progress in thermostated quartz cuvettes. The reaction medium (3 cm ) was prepared with 1.5 g/L pectin in the standard buffer and 0.063 mg of enzyme. The absorbance of the reaction mixture against the substrate blank was continuously recorded at the spectrophotometer (Perkin Elmer Lambda 2, USA). Typical reaction time was 15 minutes, but initial reaction rates were estimated considering only the absorbances recorded during the first 200 seconds, range of totally linear response. 

In order to follow progress of elimination, reactions were also performed on thin films in a special sealed glass cell which permitted in situ monitoring of the electronic or infrared spectra at room temperature (23°C). Typically, the infrared or electronic spectrum of the pristine precursor polymer film was obtained and then bromide vapor was introduced into the reaction vessel. In situ FTIR spectra in the 250-4000 cm-- - region were recorded every 90 sec with a Digilab Model FTS-14 spectrometer and optical absorption spectra in the 185-3200 nm (0.39-6.70 eV) range were recorded every 15 min with a Perkin-Elmer Model Lambda 9 UV-vis-NIR spectrophotometer. The reactions were continued until no visible changes were detected in the spectra. 

Absorption curves of the colored solutions were run on a Beckman spectrophotometer using 1.00-cm. quartz cells. A typical curve, shown in Figure 1, has an absorption maximum at about 515 millimicrons. The Coleman Junior spectrophotometer was used for routine determinations of Compound 118 throughout this study. 

Optical background, n - the spectrum of radiation incident on a sample under test, typically obtained by measuring the radiation transmitted through or reflected from the spectrophotometer when no sample is present, or when an optically thin or non-absorbing standard material is present. 

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