Double-beam spectrophotometers specifications

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... 

The performance of a spectrophotometer is dependent on a number of parameters that affect the quality of the data, namely, wavelength accuracy, photometric (absorbance) accuracy, spectral bandwidth variations, extent of stray light, and linear response of the instrument. The performance parameters can be evaluated from the specifications provided by the manufacturer. A standard list of specifications of a typical double-beam spectrophotometer is provided in Table 5. 

Since this is a book concerned primarily with applications, no further details are given concerning instrumentation. The reader is referred to Alpert et al. (1970), in which are discussed an optical diagram of a double-beam spectrophotometer operating variables (resolution, photometric accuracy) components of infrared spectrophotometers (sources, types of photometers, dispersing elements, detectors, amplifiers, and recorders) special operating features, such as optimization of scan time and available instruments and their specifications. The books by Martin (1966), Conn and Avery (1960), and Potts (1963), and the chapter by Herscher (1966) are also recommended for details on some of these topics. 

This specific type of the double-beam optical-null recording spectrophotometer is termed so because it critically balances out by the help of optical means the differential between the two beams. 

A nswer, First note that the specifications of the commercial spectrophotometers give you the degree of accuracy you can expect. This accuracy is not as good as the work reported by researchers using specially designed single-beam spectrophotometers because in commercial double-beam instruments the wavelength cams and transmission combs cannot be made as accurately as required for rotational lines, which are extremely sharp. 

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