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Dispersion Due to Detector Electronics Response Time

The response of the detector sensor and the detector electronics is not usually critical unless high speed separations are required. However, fast chromatographic analyses are often necessary when monitoring reaction kinetics and for repetitive analyses involving clinical or forensic tests. Modern solid state electronics using semi conductor devices can be designed to have an extremely fast response and the speed of the electronic signal processing is not usually the limiting factor in fast analyses. However, the sensor, can have a relatively slow response (depending on the property it is measuring) and can certainly effect the chromatographic resolution obtained with high speed separations. In the early LC UV detectors, the cadmium sulfide photo resistor was frequently employed as the UV sensor. This device was particularly slow and its response was measured by Scott et al. (12). The sensor was allowed to come into equilibrium with the light from the UV lamp and the lamp supply was switched off and the decay curve monitored by means of a high speed Bascomb Turner recorder. The results obtained are shown in figure 22.

J. Chromatogr. 186(1979)475


Figure 22. Response Curves of the Cadmium Sulfide Resistor