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The Electrical Conductivity Detectors. The electrical conductivity detector can only detect those substances that ionize and consequently, is frequently used in the analysis of inorganic acids, bases and salts. It has also found particular use in the detection of organic acids and bases that are frequently required in environmental studies and in biotechnology applications. The sensor is the simplest of all the detectors consisting of only two electrodes situated in a suitable flow cell. An example of an electrical conductivity sensing cell is

The Electrical Conductivity Detector The electrical conductivity detector measures the conductivity of the mobile phase. There is usually background conductivity which must be backed-off by suitable electronic adjustments. If the mobile phase contains buffers, the detector gives a base signal that completely overwhelms that from any solute usually making detection impossible. Thus, the electrical conductivity detector a bulk property detector. and senses all ions whether they are from a solute or from the mobile phase. In order to prevent polarization of the sensing electrodes, AC voltages must be used and so it is the impedance not the resistance of the electrode system that is actually measured. From a physical chemistry stand point the conductivity

was passed directly from the column through the detector would have a high electrical conductivity and give a large detector base current which would swamp the signal from the ions being monitored. Thus, subsequent to the mobile phase leaving the column (and after the methane sulphonic acid has achieved its purpose in producing the desired separation) the reagent must be removed to ensure that the mobile phase entering the detector only contains those ions of interest and minimal background conductivity. The methane sulphonic acid was removed by passing the mobile phase through a short reverse phase column before it entered the detector. The reverse phase will remove all organic material by adsorption due to the strong dispersive forces that will occur between the hydrocarbon chains of the reverse phase and the methyl group of the methanesulphonic acid. The ion suppression column eventually saturates and require regeneration by desorbing the methane sulphonic acid with a strong

between the tubes contained in the first PTFE sleeve. The volume of eluent in this gap can be extremely small and thus, the peak dispersion can also be made very small. The resistance of the solution situated between the tubes is inversely proportional to the electric conductivity of the solution which, in turn, is related to the ion concentration in mobile phase. Some typical specifications for an electrical conductivity detector are as follows. Typical Specifications for an Electrical Conductivity  Detector        Sensitivity 5x 10-9 g/ml Linear Dynamic Range 5 x 10-9 to 1 x 10-6 g/ml Response Index 0.97 - 1.03 The separation of a mixture of alkali and alkaline earth cations at levels of a few parts per million, shown in figure 22 gives an example of the use of the electrical conductivity detector. The cations lithium, sodium, ammonium, potassium, magnesium and calcium were present in the original

) using the numerical value of the response index. Thus. in effect, the useful linear dynamic range of a detector for quantitative purposes can be significantly extended by employing correction procedures when using the response index. It should be pointed out that the logarithmic dilution method should not be used if the linearity is to be measured by the method recommended by the E19 committee of the ASTM. Detector Response There are two ways of defining detector response, either as detector output (usually in mv) per unit change in solute concentration or as the detector output per unit change in the units of detector measurement (e.g. the sensitivity of a conductivity detector would be defined in terms of detector output per unit change in electrical conductivity). The detector response (RD) is determined by injecting a known mass (m ) onto the column and measuring the peak height (h)  in (mv), then

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