Ion chromatography on chelating stationary phases: separation of alkali metals

Analytical 250X4.6 mm I.D. columns packed with iminodiacetic acid (IDA) der ivatised silica were used to separate alkali metal ions and the ammonium io n in combination with non-suppressed conductivity detection. The addition o f 2.5-10 mmol/l of the macrocyclic crown ether 18-crown-6 to the nitric aci d eluent resulted in a change in the elution order and a significant improv ement in the resolution between potassium and ammonium because of selective complexation of potassium. However, the admixture of 15-crown-5 did not im prove the resolution of lithium and sodium, although 15-crown-5 is a select ive complexing agent for sodium. Retention and resolution of lithium, sodiu m, ammonium, cesium, rubidium and potassium ions increased at lower tempera tures down to 1 degreesC. The simultaneous separation of alkali and transit ion metals under isocratic conditions was achieved with an eluent comprisin g 10 mmol/l 18-crown-6, 1.5 mmol/l dipicolinic acid, and 1.9 mmol/l nitric acid. The chromatographic system enabled the quantitation of alkali metal i ons with detection limits in the low ppb range and excellent Linearity. Fin ally, the applicability of the method was approved by quantitation of sodiu m, ammonium and potassium in different water samples. (C) 2001 Elsevier Sci ence B.V. All rights reserved.