The detector response in isotachophoresis is usually associated with qualitative parameters such as mobility (universal detection) and molar absorbance (specific detection). A more specific response (valency) is obtained from the a.c. conductivity detector when using coated electrodes. When using UV absorption of the counter ion, a more universal character of the signal is obtained. A number of anionic and cationic operational systems are suggested. In addition, quantitative accuracy and precision are discussed with special reference to detection principless, detector cell design, driving current stability and electroosmotic disturbance.