Abstract: An improved isotachophoretic column for separating ions in a test sample is described. The column is formed from a main unitary insulating body, in which appropriate passages are formed to define (a) a pair of chambers for holding leading and lagging electrolytes, respectively, (b) a capillary through which ions of the material to be analyzed are passed in the presence of the electrolytes, (c) channels for interconnecting the electrolyte-holding chambers with opposite ends of the capillary, and (d) a channel for injecting the test sample into one end of the capillary. The capillary has a planar profile, with at least one of its parallel boundary walls defined by one region of the unitary body. The other boundary wall of the capillary is either formed from a second region of the unitary body itself, or by a surface of a separate insulating body that is attached to the main body.