Beam Spectrophotometer

The quantum leap amalgamated with qualified success in the advancement of Analytical Instruments necessitated for more rapid and precise and accurate measurements in UV and visible spectroscopy. It could be accomplished by the help of the following two cardinal modifications, namely  

In fact, the source beam is usually split in two different manners, namely  

Keeping in view, this specific, rigid and stringent requirement, the separation-in-space method is found to be normally of lower precision and accuracy than the separation-in time-method. 

Evidently, the optical choppers are quite expensive, and therefore, the instrument manufacturers very often utilize the separation-in-space method for the routine measurement spectrophotometers. 

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

---

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. 

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. 

Optical absorption (OA) absorption spectra for all the samples were collected with a CARY 5E UV-VIS-NIR or a Jasco V570 dual-beam spectrophotometers in the 200-800 nm wavelength range at the Department of Mechanical Engineering (Materials Division) in Padova (Italy). 

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... 

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 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 is meant by the precalibration of a single-beam spectrophotometer ... 

For what kind of experiment is the use of a single-beam spectrophotometer a slow, tedious process Why is it slow and tedious ... 

Can a single-beam spectrophotometer be used for rapid scanning Explain. 

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). 

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. 

---