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are the UV detector (fixed and variable wavelength) the electrical conductivity detector, the fluorescence detector and the refractive index detector. These detectors are employed in over 95% of all LC analytical applications. These four detectors will be described and for those readers requiring more information on detectors are referred to Liquid Chromatography Detectors. The subject of detector specifications will not be discussed here but will also be dealt with in detail there. Detector sensitivities and detector linearity will, however, be given for each of the four detectors. The UV Detector The UV detector is by far the most popular and useful LC detector that is available to the analyst at this time. This is particularly true if multi-wavelength technology is included in this class of detectors. Although the UV detector has some definite limitations (particularly for the detection of non polar solutes that do not possess a UV chromaphores) it has the best

The Fixed Wavelength Detector There are two types of UV detector the fixed wavelength detector and the multi-wavelength detector. A diagram of a Fixed Wavelength UV Detector is shown in figure 17.   Figure 17.�� The Fixed Wavelength UV Detector The detector consists of a small cylindrical cell (2.0 to 10.0 ml in volume) through which flows the eluent from the column. UV light from an appropriate UV lamp, passes through the cell and falls on a UV photo electric cell. In the fixed wavelength detector the wavelength of the light depend on the type of lamp that is used. There are a number of lamps available the at provide of wavelengths

The UV Detectors Although over the years a large number of LC detectors have been developed  and described, the vast majority of all contemporary LC analyses are carried out using one of four detectors, the UV detector in one of its forms, the electrical conductivity detector, the fluorescence detector and the refractive index detector. In addition, some form of the UV detector probably accounts for 80% of those analyses. The UV Absorption Detectors UV absorption detectors respond to those substances that absorb light in the range 180 to 350 nm. Many (but not all) substances absorb light in this wavelength range, including those substances having one or more double bonds (p electrons) and substances having unshared (unbonded) electrons, e.g. all olefins, all aromatics and compounds, for example, containing >C=O, >C=S, �N=N� groups. The sensor of a UV detector consists of a short cylindrical cell having a

. Only highly specific LC detectors have sensitivities that can approach those of GC detectors. See also the section on detectors in the HPLC supplement. Detector Specifications Detector specifications are like those for GC detectors and are listed as follows, 1. Dynamic Range 2. Response Index or Linearity 3. Linear Dynamic range 4. Detector Response 5. Detector Noise Level 6. Detector Sensitivity or Minimum Detectable Concentration 7. Total System Dispersion 8. Sensor Dimensions 9. Detector Time Constant 10. Pressure Sensitivity 11. Flow Sensitivity 12. Operating Temperature Range In general the specifications are the same for both GC and LC detectors with the exception of detector dispersion. Although, detector dispersion has a minimal

nbsp; It is seen that the anthracene is clearly picked out from the mixture of aromatics by the fluorescence detector and the chloride ion, not shown at all by the UV adsorption or fluorescence detectors, is monitored by the electrical conductivity detector. The simultaneous use of all detector functions make this detector very useful but, the real advantage of the trifunctional detector is that it allows the analyst a choice of the three most useful detector function in one detecting system. In addition, any of the three functions can be chosen at the touch of a switch and without any changes in hardware. An example of the use of the three individual detector function in the analysis of three quite different types of sample demonstrates

detector uses a monochromator to select the excitation wavelength and a second monochromator to select the wavelength of the fluorescent light. This instrument gives the maximum versatility and allows the maximum sensitivity to be realized for any type of solute. The system can also provide a fluorescence spectra by arresting the flow of mobile phase when the solute resides in the detecting cell and scanning the fluorescent light. The Refractive Index Detector The refractive index detector is one of the least sensitive LC detectors. It is very sensitive to changes in ambient temperature, pressure changes, flow-rate changes and can not be used for gradient elution. Despite these many disadvantages, this detector is extremely useful for detecting those compounds that are nonionic, do not adsorb in the UV, and do not fluoresce. There are many optical systems used in refractive index detectors (9) but one of the most common is the differential refractive index detector shown