Diode array spectrophotometer

The intensity of absorbed radiation. Sunlight or room lights may alter the rate of a reaction. Usually this effect is to be avoided unless the object is to study photochemical effects. The light level in an optical spectrometer that uses monochromatic light is not likely to cause problems, but if white light strikes the sample, as in a diode-array spectrophotometer, this is a possibility. 

An automated log P workstation using a shake-flask method and robotic liquid handling in 96-well plate format is commercially available [30]. The system is equipped with a diode-array spectrophotometer and equimolar nitrogen detector. 

The CLM method is a new technique, developed by Nagatani and Watarai [61]. This method produces a stable, ultrathin two-phase liquid membrane by the centrifugal force due to the rotation of a cylindrical cell, using the arrangement shown in Fig. 11. The inner diameter and inner height of the cylindrical cell were 19 and 29 mm, respectively. The rotation speed was controlled in the range 6000-7500 rpm. The summation of the absorption spectra of both interfacial and bulk organic phase species was measured in the direction perpendicular to the rotation axis with a diode array spectrophotometer. 

The quaternization kinetics were followed by 3H NMR spectroscopy using a JE0L FX-90Q NMR spectrometer. Solvolysis of p nitro-phenylacetate was followed by UV spectroscopy using a Hewlett Packard 8450 A diode array spectrophotometer. 

UV measurements were performed on an HP 8452 diode array spectrophotometer. 

What is a diode array spectrophotometer What advantages does it have ... 

A diode array spectrophotometer is one that utilizes a series of photodiodes to detect the fight intensity of all wavelengths after the fight has passed through the sample. See Figure 8.9. The advantage is that an absorption spectrum can be measured in a matter of seconds. 

The next step is to imagine having measured whole absorption spectra as a function of time, e.g. by using a diode array spectrophotometer. The kinetic traces at nl different wavelengths are arranged as columns of a matrix Y and, similarly, the molar absorptivities as columns of a matrix A, thus (4.48) transforms into... 

Consider now multivariate data, e.g. measurements at many wavelengths instead of only one, say kinetics followed by a diode-array spectrophotometer. Assume the instrument records the spectra at 1024 wavelengths. Compared with monovariate data (single wavelength), there is a dramatic increase in the number of parameters to be fitted. In addition to the rate constant, there are now 1024 molar absorptivities for each reacting component that need to be fitted. The algorithm devised so far cannot cope with that number of parameters. 

The release kinetics from the tablets of the drug-polymer complexes were carried out in buffered release media containing 0.01 M phosphate and NaCl ranging from 0.2 M to 0.02 M at 37°C by the USP basket method at 100 rpm. Drug release was monitored on a HP 8452A diode-array spectrophotometer at 250, 306, 306, 270, 278, 278, and 274 nm for sodium diclofenac and sulfathiazole, labetalol HCl, propranolol HCl, verapamil HCl, and diltiazem HCl, respectively. 

Diode-array spectrophotometers have no moving parts, or at most a shutter that moves thus they are more suited to locations near the process. However, these instruments still require the introduction of the sample into the instrument s sample cavity, as well as the necessity for a separate reference measurement. These instruments are usually only found in a single-beam configuration. 

Depending on their sensing ability, flow-through sensors can be classified into single-parameter and multi-parameter according to whether they can sense one or more analytes on passage of each sample. Multideterminations usually rely on the use of an instrument e.g. a diode array spectrophotometer) for virtually simultaneous multidetection e.g. [20]). 

A photometric flow-through sensor for the determination of carbamate pesticides (carbofuran, propoxur and carbaryl) based on similar principles as regards the detector and sensor used (a diode array spectrophotometer and a flow-cell packed with C,g resin, respectively) was employed to monitor the formation of the products resulting from hydrolysis of the analytes and online coupling of the respective phenols with diazotized sulphanilic acid. This... 

Figure 4.8 — Manifold used for implementation of the flow-through sensor developed for the determination of carbamate compounds based on hydrolysis of the analytes and dye formation, q flow-rate R reactor SV switching valve DAS diode array spectrophotometer W waste. (Reproduced from [98] with permission of the American Chemical Society).

Thus, a diode array spectrophotometer could Ise used to obtain sufficient information to elucidate both ccxnposition and sequence length. 

Figure 11.13 —Schematic am optical path showing the principle and simplified view of a diode array spectrophotometer. The shutter is the only mobile piece in the assembly, allowing subtraction of the background signal (dark current) without any light intensity striking the photodiodes. This inverted optical design allows the sample to be exposed to the exterior light. These instruments are widely used as detectors in liquid chromatography (cf. 3.7).

The ultraviolet absorption of eugenol was recorded on a HP 8452A diode array spectrophotometer. The spectrum obtained in alkaline solution (0.1 N NaOH) is shown in Figure 2, and was characterized by an absorption maximum at 296 nm. The El%/1 cm parameters of alkaline aqueous solutions have been reported as 552 at 246 nm, and 262 at 296 nm in [6],... 

Kinetic measurements were carried out using a Hewlett-Packard diode-array spectrophotometer and/or a Hi-Tech small-volume single-mixing stopped-flow instrument (fastest mixing-time 5ms) in absorbance (turbidity) mode. 

For a successful purification it is useful to remove the dyestuff from the flow and to repeat the process after some time. Because of the use of the diode array spectrophotometer and the continuous flow the irradiation time is very short. Besides the advantage of continuous purification the light induced degradation is consequently minimized. 

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