Spectrophotometer cell

Optical Applications. Vitreous siUca is ideal for many optical appHcations because of its excellent ultraviolet transmission, resistance to radiation darkening, optical polishing properties, and physical and chemical stabiUty. It is used for prisms, lenses, cells, wiadows, and other optical components where ultraviolet transmission is critical. Cuvettes used ia scatter and spectrophotometer cells are manufactured from fused siUca and fused quart2 because of the transmissive properties and high purity (222). 

Let us examine some batch results. In trials in which 5 mL of a dye solution was added by pipet (with pressure) to 10 mL of water in a 25-mL flask, which was shaken to mix (as determined visually), and the mixed solution was delivered into a 3-mL rectangular cuvette, it was found that = 3-5 s, 2-4 s, and /obs 3-5 s. This is characteristic of conventional batch operation. Simple modifications can reduce this dead time. Reaction vessels designed for photometric titrations - may be useful kinetic tools. For reactions that are followed spectrophotometrically this technique is valuable Make a flat button on the end of a 4-in. length of glass rod. Deliver 3 mL of reaction medium into the rectangular cuvette in the spectrophotometer cell compartment. Transfer 10-100 p.L of a reactant stock solution to the button on the rod. Lower this into the cuvette, mix the solution with a few rapid vertical movements of the rod, and begin recording the dead time will be 3-8 s. A commercial version of the stirrer is available. 

Spectrographically standardised substances 830 Spectrophotometer cells for, 664 data presentation, 665 double-beam, 667 layout of instruments, 666, 667 operation of, 672 radiation sources for, 664 single-beam, 666... 

Procedure. A hexane solution of Compound 118 is diluted or concentrated so as to bring the 118 content within a range of 15 to 150 micrograms per ml. In cases where the hexane solution requires concentration, the evaporation is carried out in a beaker on a steam bath with a gentle stream of air passing over the surface. The concentrated or diluted solution of 118 is washed with hexane into a volumetric flask and made up to volume with the hexane washings. One milliliter of the adjusted Compound 118 solution is precisely measured into a spectrophotometer cell, 2 drops of phenyl azide are added, and the dihydrotriazole is quantitatively formed and then treated with diazotized dinitroaniline to produce the red color as in the preparation of the standard curve. A blank, starting with 1.0 ml. of hexane and 2 drops of azide, is run at the same time. 

Samples of the chemically degraded PVC without added TFA were extracted in DCM or CH at ice temperature for one hour. The resulting solutions were filtered and after dilution aliquots were placed in spectrophotometer cells in the thermostated cell compartment of a spectrophotometer and the spectra measured at intervals over about 200 minutes. The spectra of the initial polyene solution in DCM before dilution is shown in figure 11 and successive spectra of diluted solutions in DCM and CH in figures 12 and 13 respectively. 

Spectrophotometer cell, n - an apparatus which allows a liquid sample or gas to flow between two optical surfaces which are separated by a fixed distance, referred to as the sample pathlength, while simultaneously allowing light to pass through the liquid. There are variations of this including variable-pathlength cells, and multi-pass cells, and so on. 

The highly conjugated diketo system obtained as a result of irradiation of the stilbosterol solution placed in a closed spectrophotometer cell for a duration of 10 minutes and exposed to a 15-watt short-wave ultraviolet lamp. Ultimately the extinction is duly measured at 418 nm and compared with stilboesterol (RS) treated exactly in the same manner. 

Detector Technology. For copolymer composition analysis the new diode array UV/vis detectors are extremely attractive the absorption at many wavelengths are instantaneously recorded there is only a single spectrophotometer cell so that transport time delays between detectors and axial mixing in detector cells do not confound comparison of detector response at different wavelengths and for styrene copolymers, extremely low concentrations of polymer can be detected. 

Condensation of isoniazid (isonicotinic acid hydrazide) with any a" -3-ketosteroid in acidic medium affords a yellow color conjugate, allowing the determination of 10-40 pg of the steroid [73]. The reagent is prepared by dissolving 0.8 g of isoniazid in 100 mL of methanol containing 1 mL of concentrated HCl, and then 12.5 mL of this solution is further diluted to 100 mL with methanol. To a 2 mL methanolic sample solution of the 3-ketosteroid is added 2 mL of the reagent. The mixture is allowed to stand at room temperature for an hour, and then the absorbance of the resulting colored solution is measured at 380 nm. In a 1 cm spectrophotometer cell, an absorbance of 0.3 will be produced by 42 pg of cortisone, 34 pg of prednisolone, 29 pg of prednisone, or 32.5 pg of dexamethasone [72]. 

The necessary pump powers can be achieved either by other lasers (e.g. nitrogen lasers, solid-state lasers or even focussed He-Ne- or Ar+-gas lasers) or by flash-lamps. The simplest practical arrangement is a square spectrophotometer cell, polished on all sides, containing the dye solution which is pumped by a nitrogen laser whose beam is focussed into a line parallel to and directly behind one of the cell windows. Then the Fresnel reflection from the two adjacent windows gives enough feedback in most cases, so that no additional resonator mirrors are needed and the dye laser oscillation starts. 

We undertook the study of this reaction, employing conditions where limited amounts of oxygen (or hydrogen peroxide) were allowed to react with mercaptoacetate in the presence of iron ions. The amount of Fe(III) (OH) (RS)2-2 produced was determined spectrophotometrically. Since the rate of bleaching of this complex was fast under some of the conditions, a rapid-mixing device was employed. This consisted of a spring-actuated syringe, patterned after one described by Stem and Du Bois (12), which injected one of the reaction mixtures into the other contained in a spectrophotometer cell. 

The quantum yield for H2 elimination from [Mo( y5-C5H5)2H2], measured at 366 nm in hexane solution in a degassed and sealed spectrophotometer cell, is 0.10. This value should be treated as a lower limit since reverse reaction of H2 with photogenerated molybdenocene was not prevented. This compares with a value of 0.01 that we obtained for H2 elimination from [ W(r75-CsH5)2H2] under similar photolysis conditions. 

Spectral Measurements. The ir spectra were recorded on a Perkin-Elmer 621 grating ir spectrophotometer using KBr disks prepared from ir spectroquality powder (MCB) or 0.5 mm path length, NaCl solution ir cells. Electronic absorption spectra were recorded with a Cary 17 spectrophotometer using 1-cm quartz spectrophotometer cells. Mass spectra were recorded with an AE1 MS902 mass spectrometer. 

Samples are usually placed in 1mm thick quartz spectrophotometer cells sealed with Parafilm or similar. Samples in which the aqueous phase has a very high D to H ratio are sometimes thicker, as the level of incoherent scatter due to H will be low. Samples may be in the scattering apparatus for several hours, and so H20/D20 exchange due to faulty sealing can cause errors. For gel-like samples, it is very important that there are no air bubbles trapped in the sample. Gel or viscous samples can be centrifuged to the bottom of cells, and air bubbles removed, using a Helma Roto-Vette or similar. 

The detection limit for measuring P as yellow vanadomolybdophosphoric acid is about 200 pg/L in 1 cm spectrophotometer cell and 10 pg/L when determined as molybdenum blue. 

For our eel studies a very simple technique was employed. A 1-cm spectrophotometer cell was used as an undivided electrochemical cell. It was equipped with two platinum foil electrodes which were directly connected to a sine wave generator as an ac voltage source. Much more sophisticated methods have been described in the literature (16) but this simple design permitted the observation of eel which appears at both electrodes. 

An ac electrolysis of [Ru(bipy),]Cl was carried out in a spectrophotometer cell as an undivided electrochemical cell equipped with platinum foil electrodes. Acetonitrile was used as solvent and Bu NBF, served as supporting electrolyte. The electrolysis led to the typical eel of Ru(bipy) + (20,21,23,25). Simultaneously, the complex underwent a chemical change. The spectral variations which accompanied the electrolysis (Figure 1) were very similar to those observed during the photolysis of the same solution (X. > 335 nm). The pro-... 

FIGURE 6.4 A spectrophotometer cell with an absorbing medium. I0 is the intensity of light after reflection on the front window and /t is the intensity of light not absorbed by the medium. 

Let us consider aphotochemical process (Equation 6.18) occurring with a quantum yield (f> in a photochemical reactor of a prismatic geometry, for example, a spectrophotometer cell (Figure 6.4). 

Assay since one unit of SOD activity is defined as the amount of enzyme that inhibits by 50% the rate of reduction of cytochrome c under specified conditions, it is necessary to try several different dilutions of the enzyme preparation. Solution B should be kept at 4°C and solution A warmed to 25°C a thermostatted spectrophotometer cell at 25°C should be used at 550 nm for maximum sensitivity the spectrophotometer should be set to the observed maximum absorbance when a portion of solution A is reduced with a few crystals of dithion-ite. 2.9 ml of solution A is then placed in a 3 ml cuvette and 50 /A of the enzyme sample is added with mixing. The reaction is started by adding 50 /A of solution B with further mixing and the change in absorbance at 550 nm is monitored. The enzyme sample should be replaced by water or by several standard SOD solutions to obtain a blank value, which should be subtracted, and a range of standard curves. Plots of l/AE min-1 for the standard enzyme are used to determine the activity of the unknown enzyme preparation the JE min 1 value is obtained from the linear part of the curve. 

Jlf a spectrophotometer with a cell compartment that can be temperature controlled is available, the procedure can be greatly improved and simplified. Adjust the bath temperature to 30°C, turn on the circulating pump, and wait until the cell compartment (with cell holder in place) has become stable. Then prepare a solution as described above and fill two spectrophotometer cells as soon as possible. (A third cell should already have been filled with 0.2 M HCl solution, for use as a blank.) Place the cells in the cell holder, and record the time at which the cell holder is returned to the cell compartment. Obtain absorbance readings on both samples as soon as possible these initial readings will provide values of sd. Allow about 20 min for the solutions to achieve thermal equilibrium, and then begin measuring the absorbance every 15 min. Since the runs are made sequentially rather than simultaneously, it is advisable to replace the slow run at 25°C with a run at 45°C (use 5-min intervals). Fresh solutions are needed for each temperature studied. 

Suggested design for water-jacketed Pyrex spectrophotometer cell containing iodine. The recommended material for the main part of the jacket is Delrin, which can be easily machined. The outer windows may be either glass or clear plastic. 

M21. Moreau, W. M., Spectrophotometer cells with sub-micrometre path lengths. Rev. Sci. Instrum. 41, 1251 (1970). 

For maximum accuracy, the batch method (separate solutions prepared in volumetric flasks) is preferred, but a titration method (aliquots of ligand solution added to a single solution in a spectrophotometer cell) may be necessary in some situations. Spectrophotometry permits the use of much lower concentrations of metal ion and ligand than are feasible in the pH titration method, if the molar absorptivity of the complex is high. 

C 2.0 ml NEM solution -f 0.5 ml protein solution D 2.0 ml solvent + 0.5 ml protein solution The absorbancy (Aj) of solution A (sample cell) versus solution B (reference cell), and the absorbancy (A2) of solution C versus solution D, are then determined in 1 cm pathlength spectrophotometer cells. The reaction with denatured proteins is generally rapid and complete within 10 min under the conditions specified here. Lack of further change in absorbance over an additional period of 10 min indicates that the reaction is indeed complete. 

Thin-layer chromatography was not taken seriously as a quantitative method of analysis for a long time. The comparatively simple techniques could in fact be reproduced astonishingly well but were very labour-intensive. It was common practice to scrape the separated spots off the plate together with the adsorbent layer, then to elute and to measure the extracted substances in solution. An improvement on this was the direct elution from the plate. Several elution heads are fastened above the separated spots, solvents are pumped through and the extract is collected in spectrophotometer cells. Thus, several spots can be eluted simultaneously 1. ... 

Figure 1 (left). Photograph of a spectrophotometer cell for measurements under inert atmosphere conditions. The cell pathlength is 10 mm. 

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