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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 photo�cell which, in turn, will reduce the signal�to�noise ratio and, thus, the sensor sensitivity, or minimum detectable concentration. Consequently, increasing the sensor sensitivity by increasing the path length has limitations and a well�designed 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

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

or the logarithmic dilution method. In the logarithmic method of calibration, mobile phase, now a liquid, is passed continuously through an enclosed stirred vessel containing a known mass of solute, the eluent passing directly into the detector. The logarithm of the detector output is plotted against the logarithm of the calculated solute concentration and the magnitude of the response index determined from the slope of the curve in the manner described in book 4. The response, noise and sensitivity are measured in exactly the same way as for GC detectors. Pressure sensitivity and pressure tolerance have a more important significance in LC as in multidimensional LC, the detector may be situated between two or more columns and thus must tolerate pressures up to the input pressure (e.g., several thousand p.s.i). Pressure sensitivity and flow sensitivity are also more important in LC due to the relatively high pressures involved and the sensitivity of many sensors to

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

.65) Consequently, substituting for (Vr) in equation (16) from equation (17) and for (Vo) from equation (18),   ������������������� ����������������������������������(19)   Thus (mD), the mass sensitivity of the chromatographic system depends on the detector sensitivity, column dimensions, column efficiency and the capacity factor of the eluted solute. However, irrespective of the column properties, the mass sensitivity is still directly related to the detector sensitivity. It will also be shown (see Book 22 on column optimization) that the column radius will also depend on the magnitude of the extra�column dispersion. It follows that the design of the chromatographic apparatus, the detector and detector electronics (to minimize extra column dispersion) together with the detector sensitivity will determine the mass sensitivity of the overall chromatographic system

nbsp;               Thus                   Thus. two detectors, having the same sensitivity defined as the minimum detectable change in absorbence, will not necessarily have the same sensitivity with respect to solute concentration. Only if the path lengths of the two sensors are identical will they also exhibit the same concentration sensitivity. This can cause some confusion as it would be expected that two instruments having the same spectroscopic sensitivity would also have the same chromatographic sensitivity. To compare the sensitivity of two detectors given in units of absorbence the path lengths of the cells in each instrument must be taken into account. UV