Spectrophotometers array

For quantitative analysis, the resolution of the spectral analyzer must be significantly narrower than the absorption lines, which are - 0.002 nm at 400 nm for Af = 50 amu at 2500°C (eq. 4). This is unachievable with most spectrophotometers. Instead, narrow-line sources specific for each element are employed. These are usually hoUow-cathode lamps, in which a cylindrical cathode composed of (or lined with) the element of interest is bombarded with inert gas cations produced in a discharge. Atoms sputtered from the cathode are excited by coUisions in the lamp atmosphere and then decay, emitting very narrow characteristic lines. More recendy semiconductor diode arrays have been used for AAS (168) (see Semiconductors). 

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. 

The decomposition kinetics of the N-Br-amino acids was studied spectro-photometrically by following the fall in absorbance at the wavelength of the absorbance maximum of the N-bromoamino acid, in a Milton Roy Spectronic 3000 Array or a Beckman DU65 single-beam spectrophotometer, both equipped with a cell carrier thermostated to within 0.1 °C by water flow. Kinetic experiments were initiated using a hand-driven HI-TECH SFA-12 Rapid Kinetics Accessory with a 1.00 cm flow cell. 

Diode-array UV-spectrophotometer with powerful software (although the spectra overlapped in part, quantitation could be effected in the... 

The combined use of a continuous flow system and a spectrophotometer for sample screening to discriminate between synthetic and natural colorants is also available. With a very simple flow system on a column packed with natural materials, one can discriminate natural and synthetic colorants. The natural (not retained) ones can be determined in the first step and the synthetic (retained) ones in the second step after their elution. For yellow, red, green, blue, and brown, natural or synthetic colorants were chosen as models. The specific maximum wavelength for each color (400,530, and 610 mn, respectively) was selected by a diode array system. A complete discrimination of natural and synthetic colorants was obtained for concentrations of natural colorants (in the absence of synthetic ones) up to 2000 (yellow), 2000 (red), and 10,000 (brown) times that of the detection limits (DLs) of synthetic additives. This method was applied to screen fruit drinks and candies. ... 

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. 

UV spectroscopy can be used to detect low levels of organic corrosion inhibitors in produced water. An analytic method has been developed using a diode array UV spectrophotometer [630]. 

Membrane separation coupled on-line to a flow-injection system was employed for the monitoring of propazine and terbutryn in natural water. A microporous hydro-phobic membrane was utilized in which the analytes were extracted from the aqueous medium into an organic solvent that was carried to the flow cell of a photodiode-array spectrophotometer. The LCDs were 4-5 qg so the technique could potentially be used for screening purposes. Samples with positive detection would require further analysis. 

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. 

Stopped flow mixing of organic and aqueous phases is an excellent way to produce dispersion within a few milliseconds. The specific interfacial area of the dispersion can become as high as 700 cm and the interfacial reaction in the dispersed system can be measured by a photodiode array spectrophotometer. A drawback of this method is the limitation of a measurable time, although it depends on the viscosity. After 200 ms, the dispersion system starts to separate, even in a rather viscous solvent like a dodecane. Therefore, rather fast interfacial reactions such as diffusion-rate-limiting reactions are preferable systems to be measured. 

A modern spectrophotometer (UV/VIS, NIR, mid-IR) consists of a number of essential components source optical bench (mirror, filter, grating, Fourier transform, diode array, IRED, AOTF) sample holder detector (PDA, CCD) amplifier computer control. Important experimental parameters are the optical resolution (the minimum difference in wavelength that can be separated by the spectrometer) and the width of the light beam entering the spectrometer (the fixed entrance slit or fibre core). Modern echelle spectral analysers record simultaneously from UV to NIR. 

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. 

Parallel methods using scanning 96/384-well plate UV spectrophotometers are inherently faster [292]. They will become 50-fold faster with the imminent introduction of diode-array plate readers. 

Filter-photometer or spectrophotometer incorporating prism or grating monochromator, phototube photomultiplier or diode array, glass, quartz or plastic cells. 

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

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... 

A diode array is a series of several hundred photodiodes arranged in a linear array. Single-beam spectrophotometers have been invented that utilize a diode array as the detector. In this case, the cuvette is positioned between the source and the dispersing element. Then, following the dispersion of the fight, there is no exit slit. The spray of wavelengths created by the grating fall instead across the diode array,... 

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 first measurement we make when starting a fluorescence study is not usually a fluorescence measurement at all but the determination of the sample s absorption spectrum. Dual-beam differential spectrophotometers which can record up to 3 absorbance units with a spectral range of 200-1100 nm are now readily available at low cost in comparison to fluorimeters. The wide spectral response of silicon photodiode detectors has made them preeminent over photomultipliers in this area with scan speeds of a few tens of seconds over the whole spectral range being achieved, even without the use of diode array detection. 

Finally, mention should be made of the new spectrophotometers based on an array of detectors (see Chapter 2). The operation of these spectrophotometers is much simpler, as they are not monochromators, each detector in the array being used to record a wavelength interval. However, these monochromators suffer from the drawback of poor spectral resolution. 

An HPLC detector is often a modified spectrophotometer equipped with a small flow cell, which monitors the concentration (or mass) of eluting analytes.Common detectors in the pharmaceutical laboratory are listed in Table 2 with their respective attributes and sensitivity levels. A recent survey found that 85% of pharmaceutical applications use absorbance detectors such as UVA/ is or photodiode array detectors (PDA). These two detectors are covered in more detail in this section. 

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