Ultraviolet - visible spectrophotometer

For ultraviolet/visible spectrophotometers the gratings employed have between 10000 and 30000 lines cm-1. This very fine ruling means that the value of d in equation (14) is small and produces high dispersion between wavelengths in the first-order spectrum. Only a single grating is required to cover the region between 200 and 900 nm. 

Double-beam spectrophotometers. Most modern general-purpose ultraviolet/ visible spectrophotometers are double-beam instruments which cover the range between about 200 and 800 nm by a continuous automatic scanning process producing the spectrum as a pen trace on calibrated chart paper. 

EXPERIMENTAL DETERMINATIONS WITH ULTRAVIOLET/VISIBLE SPECTROPHOTOMETERS... 

Discussion. Potassium nitrate is an example of an inorganic compound which absorbs mainly in the ultraviolet, and can be employed to obtain experience in the use of a manually operated ultraviolet/visible spectrophotometer. Some of the exercise can also be carried out employing an automatic recording spectrophotometer (see Section 17.16). 

The ultraviolet-visible spectrophotometer is the most widely used detector for HPLC. The basis of UV-VIS detection is the difference in the absorbance of light by the analyte and the solvent. A number of functional groups absorb... 

Many different detectors are used in RPLC, including ultraviolet-visible spectrophotometers (UV-VIS), refractive index (RI) detectors, electrochemical (EC) detectors, evaporative light-scattering detectors, fluorimeters, and... 

The output signal of concentration-sensitive detectors is proportional to the concentration or weight of polymer in the column eluent. Examples of this type include the differential refractometer and the ultraviolet-visible spectrophotometer. Infrared and fluorescence detectors are used infrequently. None of the detectors described above is truly universal i.e., the response of these detectors varies with the chemical species, and, in case of the DRI, response is also a function of the chromatographic eluent.156 Recently, an... 

The ultraviolet absorption spectrum of miconazole nitrate in methanol (0.0104%) shown in Fig. 3 was recorded using a Shimadzu Ultraviolet-visible spectrophotometer 1601 PC. The compound exhibited three maxima at 264, 272, and 280 nm. Clarke reported the following Methanol 264 and 272 nm = 17a), 282 nm [2]. 

Lambda 2 Ultraviolet-visible double-beam spectrophotometer Lambda 3 Ultraviolet-visible double-beam spectrophotometer Lambda 5 and Lambda 7 Ultraviolet visible spectrophotometers Lambda 9 Ultraviolet visible—near infrared spectrophotometer Lambda Array 3430 Spectrophotometer... 

Visible-spectrum studies of the course of the dye reduction were performed on a Beckmann Model 25 Ultraviolet-Visible Spectrophotometer scanning the region of 750-350 nm. 

Routine laboratory equipment Vortex mixer, 30°C shaking water bath, laboratory centrifuge, analytical balance and ultraviolet/visible spectrophotometer. 

Figure 20-2 (cQ Varian Cary 3E Ultraviolet-Visible Spectrophotometer, (b) Optical train. [Courtesy Varian Australia Ply, lid., Victoria, Australia.]... 

The basic features of ultraviolet-visible spectrophotometers are similar in many respects to those described in Section 3.1 for i.r. spectrophotometers. 

The ultraviolet (UV) absorption spectrum of donepezil in methanol was scanned from 200 to 400 nm, using UV/VIS spectrometer (Shimadzu ultraviolet-visible spectrophotometer 1601 PC). The compound exhibited four maxima at 313, 269, 230, and 209 (Fig. 3.1). Clarke [2] reported the following aqueous acid 230, 271, and 316 nm [2],... 

The UV spectrum of ciprofloxacin dissolved in methanol was recorded using a Shimadzu ultraviolet-visible Spectrophotometer 1601 PC, and is... 

When using an ultraviolet/visible spectrophotometer, instrument parameters will include wavelength and slit width. If the wavelength is changed then the measured absorbance of the sample solution is likely to change. 

Experimental. Absorbances of selected polymer and copolymer samples were measured with a Waters 440 ultraviolet absorbence detector equipped with a 254 nm filter, and a Beckman 25 ultraviolet/visible spectrophotometer. The Water s instrument was used on-line with the size exclusion chromatograph (16). The Beckman 25 was used to calibrate and standardize the Water s 440 UV detector. THF was used as standard solvent. The extinction coefficients were estimated from absorbance measurements at several polymer concentrations. The standard deviation for the absorbance measurements was typically . 001 Au for replicates on the same sample. All measurements were done at room temperature. 

Figure 26-11b shows an analogous plot of experimental data obtained with a high-quality research-type ultraviolet/visible spectrophotometer. Note that, in contrast to the less expensive instrument, absorbances of 2.0 or greater can be measured here without serious deterioration in the concentration uncertainty. 

Most modem ultraviolet/visible spectrophotometers are double beam instmments which generally covers the range between about 200 nm and 800 nm. In these instmments the monochromated beam of radiation, from tungsten and deuterium lamp sources is divided into two identical beams of equal intensity, one of which passes through the reference cell and other through the sample cell. 

Spectrometry has played in biochemistry, it may seem surprising that the first reliable commercial laboratory ultraviolet-visible spectrophotometers became available in 1940 and the first commercial infrared spec-tromefer in 1942. ... 

UV detector HPLC detector based on an ultraviolet-visible spectrophotometer using microsample flow cells (10 pi). Response to components depends on their absorption spectrum and absorptivity coefficient as defined by the Beer-Lambert law. Detector wavelength is set to give maximum sensitivity ideally at Amax however an optimum wavelength, Aopt at which all the components have a satisfactory absorbance, may be used. 

An important and widely encountered noise source, one that is proportional to transmittance, results from failure to position sample and reference cells repro-ducibly with respect to the beam during replicate transmittance measurements. All cells have minor imperfections. As a consequence, reflection and. scattering losses vary as different sections of the cell window arc exposed to the beam small variations in transmittance result. Rothman, Crouch, and Ingle have shown that this uncertainly often is the most common limitation to the accuracy of high-quality ultraviolet-visible spectrophotometers. It is also a serious source of uncertainty in infrared instruments. 

I igure 13-21 shows construction details of a typical, relatively inexpensive, manual, double-beam ultraviolet-visible spectrophotometer In this instrument, the radiation is dispersed by a concave grating, W hich also focuses the beam on a rotating sector mirror. The instrument design is similar to that shown in Tig ure 13-13c. 

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