Spectrophotometer sample chamber

Figure la. The optical arrangements of an FT-IR Spectrophotometer with reflectance attachments in the sample chamber for electrochemical experiments. (Reproduced with permission from Ref. 9. Copyright 1984 Elsevier.)... 

Some of the AP recommended experiments require the use of a spectrophotometer. A spectrophotometer is an instrument that is used to measure the amount of light absorbed (or percentage transmitted) by a particular solute in a solution. In order to determine the absorbance (A) of a sample, the instrument is set to a particular wavelength a solution, contained in a holder called a cuvette, is placed in a sample chamber and an absorbance reading is taken. This procedure may be repeated for other solutions or wavelengths. The cuvette is a standard size to ensure a given path length (b). 

A dissolution testing apparams consists of a set of six or eight thermostatted, stirred vessels of an established geometry and volume from the USP guidelines. The dissolution apparatus provides a means to dissolve each sample, but does not provide a means to determine the concentration of the aetive ingredient in the bath. In the most well-established scheme, sipper tubes withdraw samples from each dissolution vessel and send them through a multiport valve to a flow cell sitting in the sample chamber of a UV-vis spectrophotometer. In recent years, moves have been made to make in situ measurements in the dissolution baths by means of fiber-optic probes. There are three possible probe implementations in situ, down shaft, and removable in situ (see Table 4.2). 

The spectrophotometer is used to measure absorbance experimentally. This instrument produces light of a preselected wavelength, directs it through the sample (usually dissolved in a solvent and placed in a cuvette), and measures the intensity of light transmitted by the sample. The major components are shown in Figure 5.5. These consist of a light source, a monochromator (including various filters, slits, and mirrors), a sample chamber, a detector, and a meter or recorder. All of these components are usually under the control of a computer. 

The procedure for obtaining a UV-VIS spectrum begins with the preparation of a solution of the species under study. A standard solution should be prepared in an appropriate solvent. An aliquot of the solution is transferred to a cuvette and placed in the sample chamber of a spectrophotometer. A cuvette containing solvent is placed in the reference holder. The spectrum is scanned over the desired wavelength range and an absorption coefficient is calculated for each major A. ... 

Figure 25-1 9 The Spectronic 20 spectrophotometer. A photograph of the instrument is shown in (a), while the optical diagram is seen in (b). Radiation from the tungsten filament source passes through an entrance slit into the monochromator. A reflection grating diffracts the radiation, and the selected wavelength band passes through the exit slit into the sample chamber. A solid-state detector converts the light intensity into a related electrical signal that is amplified and displayed on a digital readout. (Courtesy of Thermo Electron Corp., Madison, WI.)...

Measurement of Back Reaction. The photohydrates formed in these photolyses can be dehydrated back to the uracil. This elimination reaction is catalyzed by both H30+ and OH" (4, 13, 15, 16), and at extreme values of the pH the back reaction competes visibly with the forward photolytic reaction. It was thus necessary to measure the rate constant for the back reactions under photolytic conditions. This was accomplished by photolyzing a solution in a 1 cm. cuvette in a normal manner, placing the photolyzed solution in the spectrophotometer and measuring the time variation of absorbance change, using the time drum accessory of the spectrophotometer. The temperature in the solution during photolysis and in the sample chamber of the spectrophotometer was the same,... 

Old design spectrophotometers work similar with those for UV-Vis domain, i.e. are composed of radiation somce, monochromator designed to select a desired wavelength radiation, the sample chamber and the radiation detector. In IR domain, diffuse radiation presents more serious problems then in ultraviolet and visible domain. Thus, in IR domain. 

Fig. 15 A Temperature profiles of aggregation of 20-mgmL phosphate-buffered (0.01 N, pH 3.5) water solutions of photoresponsive polymer under different illumination regimens. The correspondence between each profile and its illumination condition are indicated in plot. Turbidity was calculated from absorbance values obtained at 600 nm on Cary 50 UV-Vis spectrophotometer equipped with a thermostatized sample chamber. B and C Photomodulation of phase separation of 5-mgmL aqueous samples of photochromic polymer (T = 14°C, 0.01 N phosphate buffer at pH= 3.5). A UV-sunlight cycles. Boxes in subplot periods of irradiation UV, black boxes sunlight, white boxes. B Darkness-sunlight cycles. Boxes in subplot periods of sunlight irradiation. Reproduced with permission from American Chemical Society...

Spectra were obtained using a Digilab FTS-15E Fourier Transform Spectrophotometer. A NaCl crystal mounted in a heated cell (Model 018-5322 Foxboro/Analabs, N. Haven, Ct.) was placed in the infrared beam and the chamber allowed to purge for several minutes while the cell was brought to the desired temperature. The temperature of the cell was controlled using a DuPont 900 Differential Thermal Analyzer interfaced to the spectrometer cell. A chlorobenzene solution (ca. 10 by wt.) of the sample was then applied to the crystal using cotton tipped wood splint. 

Differential thermal analysis was performed with the DuPont 900 differential thermal analyzer the heating rate was usually 10°C. per minute. To determine heats of reaction, the calorimeter attachment to the Du Pont instrument was employed. Planimeter determinations of peak areas were converted to heat values by using standard calibration curves. For the infrared spectra either a Beckman IR5A instrument or a Perkin Elmer 521 spectrophotometer with a Barnes Engineering temperature-controlled chamber, maintained dry, was used. Specimens for infrared were examined, respectively, as Nujol mulls on a NaCl prism or as finely divided powders, sandwiched between two AgCl plates. For x-ray diffraction studies, the acid-soap samples were enclosed in a fine capillary. Exposures were 1.5 hours in standard Norelco equipment with Cu Ko radiation. For powder patterns the specimen-to-film distance was 57.3 mm. and, for long-spacing determinations, 156 mm. 

The study of the deterioration of the hydroxil groups of the catalyst and the nature of the coke that is being deposited have been studied in situ in a catalytic chamber (Spectra Tech) connected in series with a Nicolet 740 FTIR spectrophotometer. The reaction has also been carried out in an automated isothermal fixed bed integral reactor [6], in cycles of reaction-regeneration, with the aim of obtaining partially deactivated catalyst samples under contrasted operation conditions (time on stream, temperature, contact time and number of regenerations of the catalyst). 

The principle of the hollow cathode tube, production of a vapor of atoms by cathodic sputtering, has been employed by Gatehouse and Walsh (Gl) for sample vaporization. The sample is introduced into a vacuum chamber and is made the cathode which produces a cloud of activated atoms. The light of a separate hollow cathode tube is passed through this vapor and absorption is measured in a spectrophotometer. 

Reactants are pumped from storage, then heated and injected into a mixing chamber (black flow lines). Sample is added to the mixing chamber, the mixture is injected into the flow cell, and the formazan production is monitored every 15 s for 3.5 min. The mixture is flushed, the system is rinsed, and the cycle begins again. The hatched regions are maintained at surface seawater temperatures. The four solenoid valves function most of the time in normally open (NO) or normally closed (NC) positions. A Technicon Autoanalyzer pump and a Bausch and Lomb Spectronic 88 spectrophotometer were used. 

The cell density in the cultures was measured by counting with a Hemacytometer (improved Neubauer chamber) and an Olympus BH-2 compound microscope. Cells were immobilized and stained by addition of several pL of Lugol solution to a 1 mL aliquot of the culture. Pigments from cells or thylakoid membranes were extracted in 80% acetone and debris was removed by centrifugation at 10,000g for 5 min. The absorbance of the supernatant at 720, 663 and 645 nm was measured by a Shimadzu UV-visible spectrophotometer. The chlorophyll (a and b) concentration of the samples was determined according to Amon [1949], with equations corrected as in Melis et al. [1987],... 

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