Displacement electrophoresis

The method of displacement electrophoresis is described and its analogy with displacement chromatog. shown. The app. consists basically of a capillary tube, a few tenths of a mm bore and thin walled, uniting 2 vessels, each contg. an electrode. For the anal. of anions the cathode vessel contains an anion less mobile than any in the sample mixt. to be analyzed. The capillary tube is filled with a soln. of a salt of an anion more mobile than any in the sample and a buffering cation. The anode vessel contains the buffering cation. The electrodes must not produce interfering ions or gas. To reduce disturbance by electroendosmosis a long chain soluble polymer is used to increase the viscosity of the soln. in the capillary tube, and the electrode vessel is closed at the end to which electroendosmosis would cause flow if it were open. The sample is introduced between the cathode and the capillary, and a const. current is passed between the electrodes. The anions in the sample move initially at different speeds until they are sepd. in order of their mobility. Then all the anions in the app. move down the capillary at the same speed, assuming the tube to be of const. bore. The boundary between each successive pair of ions is more or less sharp, depending upon the diffusion consts., the potential gradient, the difference in mobility, and the disturbance caused by electroendosmosis, temp. difference across the capillary, and flow of liq. Each zone has a characteristic pH. Once the train of anions has sepd. it proceeds down the capillary unchanged. Since each zone has a particular potential gradient, it has also a particular rate of heat generation per unit length and a particular temp. It is thus possible to follow the sepn. by means of fixed thermocouples on the outside of the tube, which will record the fronts as they pass under the thermocouple. A thermocouple measuring the temp. of the capillary relative to its surrounding plots a series of steps on a recorder, the height of a step from the baseline being a measure of the mobility. The length of the step is preferably measured from the distance between the peaks of the record provided by a differential thermocouple measuring the difference in temp. along a short length of the tube, which gives a record which is the differential of the step curve. The length of step is proportional to the length of tube occupied by that species of ion and hence to the quantity. A qual. and quant. anal. is possible. [on SciFinder (R)]