The Electrolytic Conductivity Detector

R. C. Hall and C. A. Risk, Rapid and selective determination of free barbiturates by gas chromatography using the electrolytic conductivity detector, J. Chromatogr., Sci., 75 519 (1975). 

The electrolytic conductivity detector is a good alternative to the FPD for selective sulfur detection. The ELCD has a larger linear dynamic range and a linear response to concentration profile. The ELCD in most cases appears, under ideal conditions, to yield slightly lower detection limits for sulfur (about 1-2 pg S/sec), but with much less interference from hydrocar-... 

Use hydrogen as the reactant gas at a flow rate of 30 mL/ min, and use 1-propanol as the solvent at a flow rate through the cell of 0.5 mL/min or at the manufacturer s specified flow rate for the optimum operation of the electrolytic conductivity detector. The reactor temperature should be 900°, with a base temperature of 275°. Minimize contamination of the reaction tube by venting flow from the column at all times, except for the time during which compounds of interest elute. 

The FPD does not respond to nitrogen or halogens the AFD does, but much less so than to phosphorus. In those areas, the competition comes primarily from other types of detectors. These are the micro-coulometric and the electrolytic conductivity detectors in the nitrogen and halogen areas and, of course, the electron capture detector for chlorinated hydrocarbons and other electron-attaching compounds. 

We found the AFD, for instance, suitable for the analysis of 5-triazine herbicides, but were plagued by temperamental detector performance (52). Hartmann recently described an AFD of similar construction with vastly improved performance (35). In my opinion, the electrolytic conductivity detector has at present the best chances of making it in the nitrogen area, but the matter is far from settled. 

The electrolytic conductivity detector for gas chromatography was developed by Coulson (15, 16, 17), who described modes of operation for the detection of chlorine, sulfur, or nitrogen, but did not establish the reliability of the detector for pesticide residue analysis or the minimum detectability for each molecular species. Cassil et al. (11) described the use of the detector for determining residues of carbamate pesticides and compared its response with that of the microcoulometric detector, as mentioned earlier, finding them equal in response and selectivity and usable over a range of 3 to 200 ng of nitrogen. An improved pyrolysis tube was described, and nickel wire or turnings was used as the catalyst... 

The electrolytic conductivity detector has been used to determine organic iodine with excellent success by Westlake (20), as well as chlorine in organochlorine pesticides, operating in the reducing mode to yield HI or HCl as the detected product. The minimum detectability for chlorine is approximately equal to that of the current microcoulometric detection system. Coulson (4, 15) compared the responses of the electrolytic conductivity, microcoulometric, and electron capture detectors for organochlorine compounds in various extractives and found the first two approximately equal and the electron capture detector unsatisfactory because of high background. 

One important advantage of the electrolytic conductivity detector is its simplicity. It requires no amplification of signal, thus eliminating the electrometer necessary for the other systems. In the reducing mode, it is... 

With the electrolytic conductivity detector, compounds containing halogens, sulfur, or nitrogen are mixed with a reaction gas in a small reactor tube. The products are next dissolved in a liquid, which produces a conductive solution. The change in conductivity as a result of the presence of the active compound is then measured. In the photoionization detector, molecules are photoionized by ultraviolet radiation. The ions and electrons produced are then collected with a pair of biased electrodes, and the resulting current is measured. The detector is often used for aromatic and other molecules that are easily photoionized. 

Figure 3.25, Cross-sectional view of the electrolytic conductivity detector. (From ref. [254] John Wiley Sons, Inc).

Rapid and Selective Determination of Free Barbiturates by Gas Chromatography Using the Electrolytic Conductivity Detector J. Chromatogr. Sci. 13(11) 519-524 (1975) CA 84 69194t Erratus,... 

In the electrolytical conductivity detector (ELCD) the eluate from the GC column passes into a Ni reactor in which all substances are completely oxidized or reduced at an elevated temperature (about 1000 C). 

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