Conditions for rapid determination of inorganic cations in water by ion‐exchange chromatography and evaporative light scattering detection

The simultaneous LC determination of alkali and alkaline-earth cations is possible by ion exchange chromatography run in an isocratic elution mode, using a polymeric exchanger coated on a spherical silica gel, followed by evaporative light scattering detection. By using an aqueous trifluoroacetic acid (4 mM) isocratic eluent, a successful single run analysis of Na + , K + , Mg 2+ and Ca 2+ , was achieved in 6 min on a LiChrosil® IC CA 2 column. This method provides good linearity for the four calibration curves, and enables a 10 ng absolute detection limit for sodium, magnesium, and calcium and a 25 ng absolute detection limit for potassium, at a signal-to-noise ratio of 3. The repeatability determined from six injections was satisfactory for all inorganic cations studied. This methodology has been successfully applied to the direct analysis of mineral waters containing low levels of magnesium in the presence of high levels of calcium as well as low levels of potassium in the presence of high levels of sodium.