Spectrophotometers double beam

Double-beam spectrophotometers. Most modern general-purpose ultraviolet/ visible spectrophotometers are double-beam instruments which cover the range between about 200 and 800 nm by a continuous automatic scanning process producing the spectrum as a pen trace on calibrated chart paper. 

The absorbance and the percentage transmission of an approximately 0.1M potassium nitrate solution is measured over the wavelength range 240-360 nm at 5 nm intervals and at smaller intervals in the vicinity of the maxima or minima. Manual spectrophotometers are calibrated to read both absorbance and percentage transmission on the dial settings, whilst the automatic recording double beam spectrophotometers usually use chart paper printed with both scales. The linear conversion chart, Fig. 17.18, is useful for visualising the relationship between these two quantities. 

Procedure. The study can be carried out using either a manually operated single-beam spectrophotometer, or an automatic recording double-beam spectrophotometer. In both cases the wavelengths at which HMR and MR-exhibit absorption maxima are readily obtained from the spectra. 

Two identical reaction solutions were prepared, one at T,(= 25.000 °C) in the sample compartment of a double-beam spectrophotometer, the other at T2( = 27.170 °C) in the reference beam. A direct recording of AAbs = Absi - Abs2 was made as a function of time while the difference in reaction temperature was maintained to 0.0001 °C. Evaluate kffk and AW1 for the run shown note this calculation is possible with an arbitrary time axis. 

Pierre [60] has reported a study of the characterisation of the surface of oil slicks by infrared reflective spectroscopy. A double-beam spectrophotometer was modified for studying the reflectance spectra (at angles of incidence 45°, 60°, 70°) of oil layers (20-30 xm thick) on the surface of water using pure water as reference. 

Fourier transform spectrometer or double-beam spectrophotometer incorporating prism or grating monochromator, thermal or photon detector, alkali halide cells. 

Unikon 860 Ultraviolet visible double-beam spectrophotometer Unikon 930 Ultraviolet—visible graphics Kontron Instruments AG... 

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... 

What features of a single-beam spectrophotometer differentiate it from a double-beam spectrophotometer In what situations is it used over a double-beam instrument ... 

What are two designs of a double-beam spectrophotometer and what are the advantages and disadvantages of each ... 

Why is a double-beam spectrophotometer preferred for rapid scanning ... 

A double-beam spectrophotometer is one in which either a beamsplitter or fight chopper is used to create two beams of fight in order to deal with the problem of variable fight intensity of the different wavelengths emitted by the source. 

The above two modifications have been duly incorporated in a double-beam spectrophotometer. Figure 21.6, depicts the schematic diagram of the optical system involved in a Lambda-2 microcomputer-controlled UV-VIS Spectrophotometer (Perkin-Elmer). 

However, the most sophisticated double-beam spectrophotometer is usually pretty expensive by virtue of the following facts, namely ... 

Double beam spectrophotometers are being manufactured by various well-known manufacturers across the world, such as SUMADZU VARIAN CECIL BECKMAN PERKIN ELMER etc., to name a few. These instruments are mostly based on microcomputer-controlled devices with built-in recorder to accomplish faster speed and greater operating stability. 

Part—IV has been entirely devoted to various Optical Methods that find their legitimate recognition in the arsenal of pharmaceutical analytical techniques and have been spread over nine chapters. Refractometry (Chapter 18) deals with refractive index, refractivity, critical micelle concentration (CMC) of various important substances. Polarimetry (Chapter 19) describes optical rotation and specific optical rotation of important pharmaceutical substances. Nephelometry and turbidimetry (Chapter 20) have been treated with sufficient detail with typical examples of chloroetracyclin, sulphate and phosphate ions. Ultraviolet and absorption spectrophotometry (Chapter 21) have been discussed with adequate depth and with regard to various vital theoretical considerations, single-beam and double-beam spectrophotometers besides typical examples amoxycillin trihydrate, folic acid, glyceryl trinitrate tablets and stilbosterol. Infrared spectrophotometry (IR) (Chapter 22) essentially deals with a brief introduction of group-frequency... 

As shown in Figure B2.1, double-beam spectrophotometers automatically record the true absorbance by measuring log(IR/Is), thanks to a double compartment containing two cuvettes, one filled with the solution and one filled with the solvent. Because the two cuvettes are never perfectly identical, the baseline of the instrument is first recorded (with both cuvettes filled with the solvent) and stored. Then, the solvent of the sample cuvette is replaced by the solution, and the true absorption spectrum is recorded. 

Figure 2.29 Optical diagram of a double-beam spectrophotometer. Interchangeable lamps are available for work in the visible and ultraviolet regions and monochrornation...

EXAMPLE 1.3 If the cross section for a given transition of ions in a particular crystal is 10 cnf and a sample of thickness 0.5 mm is used, determine the minimum concentration of absorbing ions that can be detected with a typical double-beam spectrophotometer. 

Eor a typical double-beam spectrophotometer, the sensitivity in terms of the optical density is (OD)min 5x 10. Therefore, using Equations (1.6) and (1.10), the minimum concentration of absorbing centers that can be detected is... 

Figure 5. (A) Protein-difference spectrum for the binding of cellobiose onto CBH I (7.6°C). The baseline (a) was recorded (double beam spectrophotometer) with 0.720 mM cellobiose in the measuring cuvette and 0.720 mM sucrose in the reference cuvette. The difference spectrum (b) was recorded after addition of 9.3 /iM CBH I to both cuvettes.

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