Gas Chromatography Detectors - Detector Sensitivity or Minimum Detectable Concentration > Page 15


It should be noted that at the high sensitivity range settings of some commercial detectors, filter circuits are automatically introduced to reduce the noise. Under such circumstances the noise level should be determined at the lowest attenuation (or highest amplification) that does not include noise-filtering devices (or at best the lowest attenuation with the fastest response time) and then corrected to an attenuation of unity.


Detector Sensitivity or Minimum Detectable Concentration

Detector sensitivity or minimum detectable concentration (MDC) is defined as the minimum concentration of solute passing through the detector that can be unambiguously discriminated from noise. The size of the signal that will make it distinguishable from the noise (the signal–to–noise ratio) is an arbitrary choice. It is generally accepted that with electronic measuring instruments discrimination is possible when the signal to noise ratio is two and this criteria has been adopted for chromatography detectors.


Thus for a concentration sensitive detector, the detector sensitivity (XD) is given by


(Rc) and (ND) being determined in the manner previously described.