Spectrophotometer optical path

Optical reference filter, n - an optical filter or other device which can be inserted into the optical path in the spectrophotometer or probe producing an absorption spectrum which is known to be constant over time such that it can be used in place of a check or test sample in a performance test. 

The optical path of a double-beam atomic absorption spectrophotometer is depicted in Figure 26.2. The various essential components comprising the optical arrangement in Figure 26.2 are enumerated after the figure. 

Figure 26.2 Optical path of a Double-beam Atomic Absorption Spectrophotometer.

In order to measure the absorption spectra, the radical anions were generated electrochemically in the optical path of a spectrophotometer. The absorption spectrum of 3,5-dinitroanisole radical anion (Figure 11, curve c) is very similar to that of the 550-570 nm species produced photochemically. So we believe this species to be the radical anion formed by electron transfer from the nucleophile to the excited 3,5-dinitroanisole and decaying by interaction with its surroundings including the nucleophile radical cation. The behaviour described seems to be rather general for aromatic nitro-compounds since it is observed with a series of these compounds with various nucleophilic reagents. 

Except for the movable photomultiplier tube, a light scattering photometer is very nearly identical to an ordinary spectrophotometer, which measures the ratio of the intensity of transmitted light to the intensity of incident light /,//0. The absorbance per unit optical path cabs is defined in terms of this quantity as... 

UV spectra were recorded with a Unicam-SP-800-A (Pye Unicam, Cambridge, England) recording spectrophotometer, using matched quartz cells (10 mm optical path). 

A UV/VIS spectrophotometer consists of three components the source, the dispersive system (combined in a monochromator) and a detector. These components, which can be used independently to design a system appropriate for a desired application, are typically integrated into the same instrument to make spectrophotometers for chemical analysis. The sample can be placed in the optical path before or after the dispersive system (see Figs 11.2 and 11.3) and recorded spectra can be treated using a number of different computer algorithms. 

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).

Figure 11.14—Optical path between the monochromator exit and the detector for two double beam instruments (rotating mirror model and semi-transparent mirror model). Instruments with rotating mirrors are similar to those used in IR spectrophotometers. However, the light beam from the source goes through the monochromator before it hits the sample. This minimises photolytic reactions that could occur if the sample is exposed to the total radiation from the source. The optics of instruments with two detectors are simpler and only one mirror, semi-transparent and fixed, is necessary to replace the delicate mechanisms of synchronised, rotating mirrors.

Some attention must be paid to the electrode dimensions (see Fig. 9.9). The working electrode s lower edge should be close to the bottom of the cell plates to minimize iR-drop problems. The width of the working electrode in contact with the thin layer of solution should be small to minimize edge diffusion. As noted earlier, a vertical orientation is not desirable however, it is convenient and compatible with the horizontal optical path of virtually all commercial spectrophotometers. Recommended sources of cell components (including minigrids) are listed in Table 9.1. Thin-layer cells for chromatographic detection and electron spin resonance spectroscopy are discussed in Chapters 27 and 29, and their application in optical studies is described in Chapter 3. 

Hewlett-Packard (Boise, ID, USA) Model 8452A UV-VIS spectrophotometer with a quartz cell (optical path of 1.0 cm) for enzymatic activity and total protein determinations. 

All infrared spectra were recorded with an IR-PLAN microscope (IR-PLAN is a registered trade mark of Spectra Tech, Inc.) integrated to a Perkin-Elmer Model 1800 Fourier transform infrared (FT-IR) spectrophotometer. The spectrophotometer consisted of a proprietary heated wire source operated at 1050°C, a germanium overcoated potassium bromide beamsplitter, and a narrow-band mercury-cadmium-telluride (HgCdTe) detector. The detector was dedicated to the microscope and had an active area of 250 x 250 pm. The entire optical path of the system microscope was purged with dry nitrogen. 

The optical densities measured with a spectrophotometer were obtained with an optical path length equal to 1 cm. However, optical path lengths equal to 1 and 0.4 cm were used for the emission and excitation wavelengths, respectively. 

Correction for the inner filter effect The optical densities are obtained with a spectrophotometer using a path length equal to 1 cm. However, when fluorescence experiments were performed, the optical path length upon excitation was equal to 0.4 cm. Thus, the real optical density at the excitation wavelength is equal to that measured on the spectrophotometer divided by 2.5. ... 

The absorption spectra of the dyes were measured with a Shimadzu UV-3101 PC spectrophotometer (Japan) in a cell with a 1-cm optical path length. The fluorescence and fluorescence excitation spectra were studied with the use of a Shimadzu RF-5301 PC spectrofluorimeter. To study the triplet state of the dyes, apparatuses of flash photolysis with xenon lamp excitation (with an energy of 50 J and a pulse length at half maximum of xi/2 = 7 ps) [6] was used. To detect the triplet state of the dyes, the solutions were deoxygenated using a vacuum unit or purged with argon for experiments on the laser flash photolysis apparatus. A... 

A. What concentration of the cis isomer will absorb 65% of the incident 450-nm light for a cuvette (a transparent vessel used in a spectrophotometer Fig. 4-13) with an optical path length of 10 mm ... 

Fig. 7. A detailed drawing of the W-cell (Vacuum Variable path length cell). The cell mount may be attached to adaptors for the Cary model 17 or an IR spectrophotometer. The optical path goes through the center of the cell, passing through two sapphire windows and an annular opening in the calibrated handle used to turn the micrometer in order to vary the path length.

The amount of surfactant adsorbed by silica was determined by measuring the difference between the initial and final concentration of 25 ml of surfactant solution after 3 hours of contact with one gram of silica. The surfactant concentration was determined from the adsorbance at 281 nm in 10 mm optical-path quartz cells, using a double-beam Varian 634 spectrophotometer. An alternative procedure used for some cases was based upon the fact that the y-log C... 

Figure 28-18 Optical paths in a double-beam atomic absorption spectrophotometer.

Figure 9.2 Three different aspects of UV/Vis spectra. Spectra of benzene (a) in solution (a band spectrum) (b) in the vapour state (spectrum presenting a fine structure) (c) an expansion of a section from the high resolution (0.14nm total interval) line spectrum of iodine vapour. The spectrum of benzene vapour, obtained from a drop of this compound, deposited in a silica glass cuvette of 1 cm optical path, provides an excellent test to evaluate the resolution of an UV-spectrophotometer.

A spectrophotometer is designed around three fundamental modules the source, the dispersive system (combined in a monochomator), which constitute the optical section and the detection system (Figure 9.10). These components are typically integrated in a unique framework to make spectrometers for chemical analysis. A sample compartment is inserted into the optical path either before or after the dispersive system depending upon the design of the instrument. 

Figure 9.14 Simplified scheme of the optical path of a simple beam, sequential mode spectrophotometer. 1. Two co-existing sources, though only one is selected for the measurement. 2. The monochromator selects the measurement wavelength. 3. The measuring cell containing either sample or control blank is placed in the optical path. 4 and 5. Diode detector and control diode.

Figure 9.16 Optical path from the exit of the monochromator to the detector for two double beam instruments, (a model with two rotating mirrors and a model with a semi-transparent mirror). The arrangement of the apparatus with rotating mirrors is similar to that of IR spectrophotometers apart from the fact that the light beam issuing from the source passes first through the monochromator before it hits the sample. In this way the photolytic reactions which could occur owing to an overexposure to the total radiation issued from the source are minimized. A more compact and simple optical assembly with a single beam associated with two detectors. A semi-transparent and fixed mirror replaces the delicate mechanism of synchronized, rotating mirrors.

Figure 10.8 The optical assembly of a Fourier transform apparatus, (a) 90° Michelson interferometer with below, some details of the beam-splitter (b) the optical diagram of a single beam spectrophotometer (picture of Shimadzu model 8300). A low power He/Ne laser is used as an internal standard (632.8 nm) in order to locate with precision the position of the mobile mirror by an interference method (this second sinusoidal interferogram which follows the same optical pathway, is used by the software to determine the optical path difference).

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