Extra Column Dispersion - Dispersion Due to Detector Electronics Response Time > Page 47


The curve shows very significant a.c. noise, which was smoothed by a 5-point smoothing routine available in the recorder software and the smoothed curve is included in figure 22. The smoothed curve is also shown expanded to full scale together with the logarithm of the expanded curve. From the slope of the linear portion of the logarithmic curve the time constant of the sensor could be calculated and was found to be about 2.5 s. A time constant of this magnitude is completely unacceptable for high speed liquid chromatography as a complete separation can be achieved in a period commensurate with the time constant of the cadmium sulfide detector.

Solid state photo sensors are much faster than the cadmium sulfide photo resistor but the fastest sensor appears to be the photo multiplier, such as the IP-28 or similar type. The same experiment was carried out using the photo multiplier and the decay curves obtained are shown in figure 23. It was found necessary to operate the light source on d.c. as the 60 Hz noise was so great it swamped the sensor response.

J. Chromatogr.186(1979)475


Figure 23. Response Curves of the IP-28 Photo multiplier