Single-Beam Spectrophotometry

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... 

Ultraviolet spectrophotometers cont.), single-beam, 225 standardisation, 226 Ultraviolet spectrophotometry, 221-232 absorption cells, 226 colorimetry, 228 derivative, 230 difference method, 229 dual-wavelength, 229 identification by, 231 influence of pH, 224 influence of solvent, 224 laws of absorption, 222 quantitative applications, 227 stray-light effects, 224 Ultraviolet-visible detector, 202 multiwavelength, 211 Unicontin, 1011 Unidiarea, 474 Unidone, 356 Uniflu, 557, 893 Unilobin, 709 Unimycin, 846 Uniphyllin, 1011 Uniprofen, 677 Unisom, 576... 

Spectrometers that use phototubes or photomultiplier tubes (or diode arrays) as detectors are generally called spectrophotometers, and the corresponding measurement is called spectrophotometry. More strictly speaking, the journal Analytical Chemistry defines a spectrophotometer as a spectrometer that measures the ratio of the radiant power of two beams, that is, PIPq, and so it can record absorbance. The two beams may be measured simultaneously or separately, as in a double-beam or a single-beam instrument—see below. Phototube and photomultiplier instruments in practice are almost always used in this maimer. An exception is when the radiation source is replaced by a radiating sample whose spectrum and intensity are to be measured, as in fluorescence spectrometry—see below. If the prism or grating monochromator in a spectrophotometer is replaced by an optical filter that passes a narrow band of wavelengths, the instrument may be called a photometer. 

Spectrophotometry. The analytical reagents were prepared as described by Draganic et al. (5) and the analytical procedure was checked by preparing a set of 0.1, 0.2, and 0.3 mM oxalic-acid complex solutions. The measurements were carried out on a Cary model 15, dualbeam spectrophotometer (Natick) and on a Zeiss PMQII single-beam spectrophotometer (Riso), both with temperature-controlled cell compartments. 

The spectrometer system for AAS can be configured as a single-beam system, as shown in Fig. 6.8, as a double-beam system, shown in Fig. 6.14, or as a pseudo-double-beam system, which will not be discussed. (See the reference by Beaty and Kerber for a description of this system.) Note that in AAS the sample cell is placed in front of the monochromator, unlike UV/VIS spectrometers for molecular absorption or spectrophotometry, where the sample is placed after the monochromator. 

This book has wide variety of topics in spectroscopy including spectrophotometric apparatus and techniques. Topics covered absorption, emissions, scattering, causes of non-linearity, monochromators, detectors, photocells, photomultipliers, differential spectrophotometry, spectrophotometric titration, single beam, dual and multi wave length spectrophotometry, and diode array spectrophotometers. 

The typical nowadays system for the detection of transient absorption in solution has the optical scheme represented in Fig. 8.1. It is based on single beam spec-trophotometric time resolved detection of light transmitted by the sample at single wavelengths (kinetic spectrophotometry). 

Optical Properties The optical properties of the films were measured by single-beam UV-Visible spectrophotometry (Perkin Elmer Lambda 35). The films were deposited on fused quartz slides to avoid substrate curvature issues in the polymeric films. 

Instruments with single and double beam optics are available. The double beam optical arrangement Is more or less similar to that of double beam apparatus in absorption spectrophotometry. 

The technique of detection via light absorption [9] exploits results from UV-visible spectrophotometry, especially in the use of monochromatic radiation and a reference system. This requires the presence of at least two fibers, to separate the outward and inward light beams, and so this method is rarely used. In contrast, fluorescence [10] can be measured directly using a single fiber and very low concentrations can be detected. Furthermore, coupling the immobilized enzyme on an optical fiber with a fluorescent cc actor, such as NADH, opens up greater possilnlities. The system is even simpler in the case of bio/chemiluminescence because the reference and excitation beams are obsolete, and the light can be emitted directly to the sensitive component [11]. The excellent quantum yield of bioluminescence also facilitates the detection of low concentrations. 

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