Single-beam grating instruments

A further advantage of spectrophotometers is the ready availability of a number of low-cost instruments with sufficient accuracy and reproductivity for dyebath analysis. Much of the work in the current study was carried out on a single-beam grating spectrophotometer costing approximately 2,000. The computations necessary in the analysis can be conveniently carried out on low-cost desk calculators or microprocessors. The calculations necessary for a four-dye mixture (or three dyes plus background) can be handled on a system costing less than 1,000. The least-squares fit of 16 points of the absorption spectrum can be carried out on a 3,000 minicomputer. Development of these low-cost instrument-minicomputer systems is largely responsible for consideration of dyebath reuse as a practical reality for the textile industry. 

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. 

Simultaneous multicomponent determinations, 361 Sine waves, 33, 34, 508,956 mathematical description, 135 superposition. 137 Single-beam computerized spectrophotometers, 358 grating instruments, 357 instruments, 240, 241, 351 for atomic spectroscopy, 240 efl ect of mismatched cells, 343 for molecular absorption measurements, 351 advantages, 358 Singlet state, 216, 400-402,411 excited, 216,400,401,405 Size distributions, measuring, 951. 955, 961... 

An illustration of the single-beam resolution of the instrument is shown in Fig. 6. The 140 cm water vapor bands are in a spectral region where there is a decrease in reststrahlen plate and grating... 

Because a CCD is a two-dimensional array of pixels, it is possible to create a double-beam instrument with a single detector. Coupled in an optical design with an imaging grating, the output of two fibers may be imaged simulfaneously and separately onto the CCD and both spectra readout by the electronics. 

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