Simultaneous separation of common mono- and divalent cations on silica gel modified with aluminium by non-suppressed ion chromatography with conductimetric detection and nitric acid–15-crown-5 as eluent

The modification of silica gel with aluminium by a coating method was very effective for the preparation of silica-based stationary phases which acted as a cation exchanger under strongly acidic conditions. However, the separation of common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) on an aluminium-adsorbing silica (Al-Silica) column was moderate by a conductimetric detection ion chromatography (IC) with strongly acidic eluents. Then, the addition of various crown ethers (12-crown-4, 15-crown-5 and 18-crown-6) in acidic eluent was carried out. As a result, it was found that 15-crown-5 was most effective for the improvement of peak resolution. Excellent separation of these cations was achieved in 20 min by elution with 2 mM nitric acid–2 mM 15-crown-5. The proposed IC was successfully applied to the determination of major cations in various natural waters.