Spectrometers UV-visible

What material is the sample tube made of Just like a cuvette in a UV-visible spectrometer has to be optically transparent, the EPR sample tube must be transparent for the magnetic component of microwaves. High-quality quartz is the preferred construction material low-quality quartz and especially any type of glass will not... 

Fluorimeters have similar components to UV/visible spectrometers but differ in the geometry of the radiation beams and in the need to be able to select or scan both excitation and emission wavelengths. 

Like much instrumentation working in the IR/visible/UV region of the spectrum, most modern UV/visible spectrometers are of the dual-beam type, since this eliminates fluctuations in the radiation source. The principle of this has been described in detail in Section 3.2. Radiation from the source is split into two by a beam splitter, and one beam is passed through the sample cell (as in a single beam instrument). The other beam passes through a reference cell, which is identical to the sample cell, but contains none of the analyte... 

Fluorescence spectrometers are equivalent in their performance to singlebeam UV-visible spectrometers in that the spectra they produce are affected by solvent background and the optical characteristics of the instrument. These effects can be overcome by using software built into the Perkin-Elmer LS-5B instrument or by using application software for use with the Perkin-Elmer models 3700 and 7700 computers. 

Absorbance measurements were made by using a Cary IE UV-visible spectrometer (Varian, France), while circular dichroism spectra were recorded with a Jobin-Yvon Mark V dichrograph, both at 20°C, after dilution in water. 

Figure 11.12—Schematic ant optica path of a single beam spectrophotometer equipped with electronic regulation (Hitachi U-1000). Measurements in solution are often carried out at a fixed wavelength after a calibration curve has been plotted. The use of higher performance double beam UV/Visible spectrometers is not necessary for these measurements in which the spectrum is not recorded. On the other hand, quantitative measurements from mixtures represent a different type of analysis.

CPs of copolymers can be determined using the optical transmittance method (Chung et al., 1999), and even using a visual observation method (Pandya et al., 1993). Optical transmittance of aqueous polymer solutions at various temperatures can be measured using a UV/visible spectrometer. Sample and reference cells are thermostated with a circular water jacket, and the sample is monitored for the onset of turbidity. For the visual observation method, copolymer solutions at different concentrations are measured by heating them in glass tubes immersed in a well-stirred heating bath. The temperature of Lrst appearance of turbidity is taken as the CP. For both methods, the samples must be well-stirred. 

Reflectance. Both internal and external reflectance spectroscopy are relatively simple experiments to perform. Commercially available attachments for standard UV-visible spectrometers can be used. For films with strong electronic transitions reasonable spectra can be obtained. The theory for external and internal reflectance is the same as that for the IR and can be found elsewhere (2, 37). The techniques have not been very popular in their applications to surface analysis. The major reason appears to be... 

Principal component analysis is most easily explained by showing its application on a familiar type of data. In this chapter we show the application of PCA to chromatographic-spectroscopic data. These data sets are the kind produced by so-called hyphenated methods such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) coupled to a multivariate detector such as a mass spectrometer (MS), Fourier transform infrared spectrometer (FTIR), or UV/visible spectrometer. Examples of some common hyphenated methods include GC-MS, GC-FTIR, HPLC-UV/Vis, and HLPC-MS. In all these types of data sets, a response in one dimension (e.g., chromatographic separation) modulates the response of a detector (e.g., a spectrum) in a second dimension. 

Clinical chemists analyze blood and urine to determine the concentrations of hormones, metabolites, and other substances to diagnose illnesses rapidly and accurately. The central instrument in a modern blood analyzer is a UV-visible spectrometer. 

Ultraviolet Spectroscopy The ultraviolet spectra of aromatic compounds are quite different from those of nonaromatic polyenes. For example, benzene has three absorptions in the ultraviolet region an intense band at Amax = 184 nm (e = 68,000), a moderate band at Amax = 204 nm (e = 8800), and a characteristic low-intensity band of multiple absorptions centered around 254 nm (e = 200 to 300). In the UV spectrum of benzene in Figure 16-19, the absorption at 184 nm does not appear because wavelengths shorter than 200 nm are not accessible by standard UV-visible spectrometers. 

The results of pH, DR, and chloride ion analysis by HPLC, pH meter, IC and UV-visible spectrometer at time interval ... 

Figure 5.1 Automatic sample deposition device for TLC and a system to read the plate. Left, programmable applicator Linomat IV. Right, densitometer measuring the light either reflected or transmitted by the plate. The optical set up is similar to that of a UV/visible spectrometer (model Scanner 3, reproduced courtesy of Camag).

Fluorimeters have similar components to UV/visible spectrometers but... 

Figure 1.15 This UV-visible spectrometer (UVIZ) is used to measure ozone and other stratospheric gases during the dark winter months in Antarctica. 

Proton nuclear magnetic resonace ( H NMR) spectra were recorded in DMSO-d or trifluoroacetic acid (TFA-di) solution on a Varian EM-360L 60-MHz NMR spectrometer, chemical shifts are repotted in parts per million from internal tetramethylsilane (TMS). Ultraviolet (UV) spectra were recorded on a Gilford Response UV-visible spectrometer using deionized water as solvent Infrared (IR) spe were recorded on a Beckman AccuLab 8 spectrometer and were calibrated with the 3027.9, 1601.8, and 1028.3 cm bands of polystyrene. Potassium bromide (KBr) disks of herbicide-cyclodextrin complexes and of propoitional mechanical mixtures of heibicide and cyclodextrin were prepared for the analysis. 

The micro flow system used for this measurement is basically the same as given in figure 1. Next to the sample and wash pumps, two additional pumps are used to supply solutions of molybdate and ascorbic acid. Between the pumps and the detector, a mixing coil of approximately 30 microliters is located. Here the reaction mixture is held for 40 seconds to let the reaction proceed before it is flushed back through the detector. The detector is a capillary detector cell of 1 mm pathlength, inter ced to a UV-visible spectrometer by means of optical fibers. The setup of the system is given in Figure 6. 

Once a colorant has been chosen for a particular pH range, it is desirable that the colorant maintain its depth of shade over the lifetime of the formulation. Extremes of pH can initiate decomposition of some sensitive colorants and so it is best to confirm the pH stability of each candidate. The pH stability can be monitored by measuring the color strength of the sample over time using a ultraviolet (UV)-visible spectrometer or colorimeter. (We will discuss instrumentation more in a later section.) This measurement is usually made periodically over several weeks. 

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