i.e.    Thus, a knowledge of (NP) can be used in detector design when a particular sensitivity is the objective.   Flow Sensitivity Flow sensitivity is another detector property that can have a significant effect on long term noise and, consequently, also on the detector MDC. Again it is the bulk property detectors that are the most likely exhibit high flow sensitivities (e.g., the katharometer). To reduce its flow sensitivity, the katharometer is usually fitted with a reference cell through which a flow of mobile phase also passes. The two sensors for the column flow and the reference flow are placed in the arms of a Wheatstone bridge so that any changes in flow rate are to a large extent compensated. The flow sensitivity (DQ) is defined in a similar manner to pressure sensitivity (i.e. mV/ml/min). The flow sensitivity can be used to calculate the flow change (NQ) that would  provide a signal equivalent

a small sensor volume, it follows that the radius of the sensor cell must also be reduced as (l) is increased. This results in less light falling on the photoÐcell which, in turn, will reduce the signalÐtoÐnoise ratio and, thus, the sensor sensitivity, or minimum detectable concentration. Consequently, increasing the sensor sensitivity by increasing the path length has limitations and a wellÐdesigned cell involves a careful compromise between cell radius and length to provide the maximum sensitivity. Most modern UV spectrometer sensor's have path lengths that range between 1 and 10 mm and internal radii that range from about 0.5 to 2 mm. From equation (2), It is seen that the sensitivity of the sensor as measured by the transmitted light will be directly proportional to the value of the extinction coefficient (k) and the path length of the sensor cell (l). It follows, that to increase the sensitivity of the system for a given substance having a given extinction coefficient (k

, is not normallyaproblemingeneralchromatographicanalysis. Thismay involve careful magnetic screening to reduce the effect of stray, low-frequency electromagnetic fields from nearby power supplies and any high energy consuming laboratory equipment. Pressure Sensitivity The pressure sensitivity of a detector can be very important as it is one parameter that determines both the long term noise and the drift. As it influences long term noise, it will also have a direct impact on detector sensitivity or minimum detectable concentration. Some detectors are more sensitive to pressure changes than others. The katharometer detector, which is used frequently for the detection of permanent gases in GC, can be very pressure sensitive. Careful design can minimize the effect of pressure. It should be noted that all bulk property detectors will tend to be pressure sensitive. The pressure sensitivity (DP) should be given as the output in millivolts for unit pressure change in the detector (

property being measured that will provide a signal equivalent to twice the noise. The sensitivity defined in concentration units is, in general, more useful to the analyst.   7.Detector Dispersion – () – This is generally not significant in GC detectors   8. Detector Time Constant – (Dt) – The overall time constant of the sensor and electronics is given in milliseconds. It is of interest in high speed chromatography.   9. Pressure Sensitivity - (DP) – The pressure sensitivity of a detector is the output that results from unit change in pressure. It is usually specified in V/p.s.i. or V/kg/m2 . It is important in detector design. 10. Flow Sensitivity – (DQ) – The flow sensitivity is the output that results from unit change in flow rate. It is specified in V/ml/min. It is important in detector design. 11. Temperature Sensitivity – (DT) – Thetemperaturesensitivityisdefined as the output that results from 1oC change in temperature. It is given in V/oC

nbsp; 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

Temperature Sensitivity Detector temperature sensitivity varies greatly from one detector to another. The FID used in GC is virtually insensitive to temperature changes but this may not necessarily be true for the associated electronics. In contrast the katharometer detector is extremely sensitive to temperature changes (the reason for this will be clear when the katharometer detector is discussed) and must be thermostatted in a separate oven. Temperature changes together with changes in flow rate are the