Simultaneous determination of low concentrations of ammonium and potassium ions by capillary type isotachophoresis.

Low concentrations of ammonium and potassium ions (<2.0 mg/l.) were determined simultaneously by capillary type isotachophoresis based on the interaction between potassium and 18-crown-6 in the aqueous leading electrolyte. The PU value of potassium ion increased with increasing concentration of 18-crown-6 up to 3mM, whereas that of the ammonium ion remained almost constant. Thus complete separation of ammonium and potassium ions could be obtained by using 1-3mM 18-crown-6. The error in the analysis of mixtures containing ammonium and potassium ions (250-mul sample injection) was less than +/- 20% with a leading electrolyte containing 3mM 18-crown-6. The analysis time was 18 min.