Direct Log Ratio Recording, Rapid Scanning Spectrophotometer Jerzy W. Strojek, Gary A. Gruver, and Theodore Kuwana Department o j Chemistry, Case Western Reserce UniGersity, Cleoeland, Ohio 44106
A double beamed, direct log ratio recording, rapid scanning spectrophotometer (RSS) which scans the wavelength range of 3700 to 7000 8, or any width of that range at repetitive velocities up to 4000 Hz has been built in our laboratory. The signal-to-noise ratio, wavelength resolution, and absorbance sensitivity depend on the scan velocity, but absorbance changes of less than 0.02 unit and a resolution of 20 A at a scan rate of 1000 Hz have been obtained. Instrumental design and capabilities are discussed. The use of the RSS for following intermediates and products during electrolyses at optically transparent electrodes is presented. RECENTINTEREST in spectrally monitoring and characterizing transient intermediates produced during electrolyses at optically transparent electrodes (OTE) ( 1 , 2 )has led to the development of a rapid scaning spectrophotometer (RSS). The advantages of this RSS are simplicity of design (Figure 1) and operation (Figure 2), with easy fabrication from available components, direct absorbance readout, and versatility of selecting scan ranges and scan times. In this instrument, scanning is made possible by a vibrating mirror similar to a design reported by Niesel et al. (3). The capabilities and instrumental features of recently available RSS have been summarized by Pimentel(4). PRINCIPLES
The main features of this instrument are (1) optical elements arranged with the image of the entrance slit focused at the exit slit; (2) vibrating concave mirror reflects light at variable angles to a plane grating; (3) exit beam split and monitored by two matched photomultiplier tubes (PMT), one as a reference; and (4) outputs of PMTs fed into a differential log ratio amplifier for absorbance readout. Optical Scheme. As shown in Figure 1, the Cassegrainian spherical mirrors C (Bausch & Lomb) collect and collimate the emission from the source element (Phillips, 55W quartz iodide lamp). Lens L i (all lens are fused silica or quartz) (1) J. W. Strojek and T. Kuwana, J. Electroanal. Chem., 16, 471 (1968). (2) J. W. Strojek and T. Kuwana, Dis.Faraday Soc., 45, 134 (1968). (3) W. Niesel, D. W. Lubbers, D. Schneewolf, J. Richter, and W. Botticher, Rev. Sci. Instrum., 35, 578 (1964). (4) G. C. Pimentel, Appl. Opt., 7, 2155 (1968).
focuses the radiation from the Cassegrainian C on the entrance slit S 1. The vibrating mirror M (concave, fl
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