A New Potential Gradient Detection System for Isotachophoresis

Abstract

Concerning the potential gradient detector for isotachophoresis, the authors solved the problem of bubble generation on the sensing electrodes which frequently resuls in suspension of isotachophoresis, which had been the biggest impediment to the practical development of this type of detector.

In order to obtain stable measurements of zone boundaries without descernible generation of bubbles even at 250 μA of migration current, several modifications were made. The projecting part of the sensing electrodes were scraped off resulting in reduction of the electric current between two sensing electrodes, the cross-sectional area of the cell was expanded resulting in reduction of the current density in the sensing cell, and finally, the sensing cell, which is situated at a high voltage to ground, was isolated from ground potential by converting the electrical signal provided by the sensing cell into an optical signal, resulting in a reduction of the current to ground.

The detection limit was 2×10⁻⁹ gram equivalent for adipic acid. A boundary between zones was detectable when the mobility difference between the zones was about 1% in the case of a sample having a diffusion coefficient of about 10⁵ cm²/sec.

Key Words:

• isotachophoresis
• potential gradient detector
• sensing cell
• sensing electrode
• leading electrolyte
• terminal electrolyte