Rapid scanning spectrophotometer

Generally, measurement of absorption spectra of the colored form of spirobenzopyran is very difficult using normal spectrophotometry, as the colored form is thermally unstable. The absorption spectra of the colored form of 6,8-dinitro-BIPS 7, which is exceptionally stable in DMSO even at 23°C, are shown in Figure 1.4. Generally, it is possible to obtain a reasonable absorption spectrum of the colored form by the use of a rapid scanning spectrophotometer. 

A number of stopped-flow systems are commercially available. Three of the most used are manufactured by Atago Bussan (formerly Union Giken), Japan Dionex (formerly Durrum), USA and Hi-Tech Scientific, UK. These also manufacture rapid scan spectrophotometers, multimixer, temperature-jump and flash photolysis equipment. 

These methods of obtaining complete ultraviolet-visible spectra can be very time-consuming. However, rapid scanning spectrophotometers based on optical diode array detectors are now eormnereially available and are capable of recording complete spectra in very short time intervals (1 second or less). They can therefore be used to obtain spectra of separated components without stopping eluent flow or to detect at several wavelengths simultaneously. 

Rapid-scanning Spectrophotometers. These en loy multi-channel detectors. The most commonly encountered detector of diis t e is tlie linear photodiode array. The reversed-optics mode is employed, so that radiation is passed throu tiie sample or reference cell, tiien dispersed by a dif action grating polychiomator integrated intensity of radiation incident on it which is determined by tiie spectial dispersion photo ode ratio. If, for example, a 200-nm txmdwidtii of radiation were dispersed across 256 photodiodes, tiie nominal resolution per photodiode woitid be 0.78 nm. 

The reaction mechanism was also confirmed by a series of absorption spectra recorded on a rapid-scan spectrophotometer. 

Using optically transparent electrodes and a rapid scan spectrophotometer Gruver and Kuwana (1972) obtained ATcomp = 3 x 1012 for the dimethyldihydrophenazine cation radical and 6 x 106 for the methylviologen cation radical [11]. 

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