The invention relates to isotachophoretic columns for the ionic analysis of a test sample.
In known types of isotachophoretic columns, which are useful in the quantitative analysis of chemical samples, a pair of reservoirs or chambers that respectively hold diverse types of electrolytes (identified as "leading" and "lagging" electrolytes, respectively) are selectively connected to opposite ends of a capillary tube which is generally wound around a metallic cylinder for thermostatic purposes. The introduction of a test sample into the capillary in the presence of communication between the electrolyte chambers and the ends of the capillary is effective, when a high voltage is applied between electrodes positioned in the electrolyte chambers, to cause a discrete migration of the separate types of ions in the test sample through the capillary in succession in one direction. A suitable detecting device coupled to the ionic flow through the capillary records the pulse-like transition in signal level indicative of the passage of the successive ion types past the measuring point and conveys such signals to a suitable recording device to form an isotachophoregram.
Presently known designs of this type have several disadvantages. In general, they employ removable hoses and threaded couplings between the electrolyte reservoirs and the respective ends of the capillary, which results in inevitable gaps and dead spaces within the apparatus. Such gaps lead to uncontrolled out-diffusion of the test sample and electrolyte, thereby deleteriously effecting both the speed and accuracy of the measurements, and also exhibit regions of extremely high resistance to the flow of ionic current established by the high voltage applied to the electrodes of the electrolyte chambers.
In a similar manner, the frequent deformations and the lack of dimensional stability inherent in the use of elastic hoses and elongated glass or plastic capillary tubes adversely affects the establishment of the proper electrical gradients that affect the separation of the ions in the capillary, and also leads to poor cooling of the capillary and the associated detection facilities.
Also, the amplitude of the applied electrical voltage, and thereby the speed and efficiency of the ionic separation, is limited in such present designs because of the relatively poor electrical insulation that naturally results by interconnecting, via deformable and dimensionally unstable components, the separable subassemblies of the known types of isotachophoretic columns.