Gas Chromatography Detectors - Early Gas Chromatography Detectors > The Emissivity Detector > Page 29
Opposite the flame was situated a lens that focused the light emitted onto a photo cell. The output from the flame light was balanced out by a simple potentiometer network and the signal passed to a potentiometric recorder. The detector gave a partially selective response to aromatic hydrocarbons or any solute that either increased the luminosity or imparted color to the flame. The sensitivity varied widely with the solute being detected. Aromatics that impart strong luminosity to the flame giving a strong response and consequentlyahighsensitivity (ca 1 x10-6 g/ml).
Conversely, saturated hydrocarbons impart little luminositytotheflameandthushave a weak response and a very low sensitivity–the very features for which the detector was designed. The linear range is difficult to determine from the original publication but appears to be in excess of two orders of magnitude. The performance of the detector is illustrated in figure 11.
The development of these early detectors not only helped establish GC as a viable analytical technique but also stimulated the development of other types of vapor sensing devices. The future detectors would prove to have extremely high sensitivities and wide linear dynamic ranges and to function on widely different principles. However, with the exception of the katharometer, they wouldalso rendertheseearlydetectors virtually obsolete. Nevertheless, they played an important role in the early days of GC and in their time were exciting devices to operate.