Cell detector, dispersion effect

We have prepared the 8x8 organic photodiode matrix without organic transistors. The effective sensing area of each sensor cell is 50 x 50 pm2 and periodicity is 100 pm, which corresponds to 250 dpi. The dispersion of photocurrent of photodiodes with illumination of light (80 mW cm-2) is shown in Fig. 16.9 under light illumination of black and white areas. We have positioned a sheet of paper with a white capital letter T prepared by a laser printer on the photodiode matrix and measured the photocurrent of each detector with light illumination (80 mW cm-2). The mapping of photocurrents is shown in Fig. 16.9b. 

Many detection principles require a finite volume of eluent. For example, a UV absorption detector yields a signal that is directly proportional to the optical pathlength (Beer s law, see eqn.5.21). The volume of the detector flow cell is usually well-defined and its contribution to aejc, and hence its effects on the observed dispersion ctg, can be discussed in quantitative terms (see section 7.4.2). 

Some detectors employ the optothermal effect the absorbed modulated infrared radiation heats the sample and its environment, thus producing sound waves which are recorded with a microphone. They can be combined with scanning spectrometers and interferometers. A Golay cell (Golay, 1949) measures the optothermal pressure change by a light beam which is deflected by a reflecting membrane. The first infrared process spectrometer, the URAS, alieady employed the absorption bands of a detector gas to specifically analyze the concentration of this particular gas in a sample. This is a non-dispersive spectrometer already mentioned in Sec. 1. 

The small length-to-diameter ratio is in conflict with the premises adopted in the development of the Golay equation for dispersion in an open tube and consequently its conclusions are not pertinent to detector sensors. Atwood and Golay [17] extended the theory of dispersion in open tubes to tubes of small length-to-diameter ratio. The theory developed is not pertinent here as it will be seen that dispersion from viscous sources is negligible. Nevertheless, the effect of the cell on solute profiles is shown in figure 10. Fortunately, this situation rarely arises in practice as the profile is further modified by the manner of entrance and exit of the mobile phase. 

Fig. 15. Rotatory artifacts that simulate Cotton effects at an absorption band. The dependence of the rotatory artifact on absorbance of p-cresol solutions placed in series with the same poly-L-glutamic acid solution is shown. The concentration of p-cresol was adjusted to give the total absorbance of chromophore plus polypeptide background that appears with each curve. The rotator, poly-L-glutamic acid, was at concentration of 0.5% at pH 7.0 in a 10-cm cell. The rotations are those actually observed, a, in degrees. The rotatory dispersion at Am 2 coincides almost exactly with that for the polypeptide alone, so that it has been omitted from the figure. At Am 4, an interference filter, /, with maximum transmission between 280 and 285 m/i, was placed in the optical path. The absorption spectrum, in arbitrary units, is typical of p-cresol plus poly-L-glutamic acid background. The emission spectrum is represented in arbitrary units, uncorrected for detector response. (Urnes et al., 1961a.)...

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