Ion chromatographic separation of common mono- and divalent cations on an unmodified silica gel column by elution with oxalic acid containing crown ethers

Abstract

An unmodified silica gel (Zorbax BP-SIL) column (150 × 4.6 mm id) was applied to ion chromatography (IC) with conductimetric detection of common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). The retention behavior of these mono- and divalent cations on the column under acidic eluent conditions was investigated and it was found that the Zorbax BP-SIL behaved as a cation-exchange stationary phase under acidic eluent conditions and incomplete separation of these mono- and divalent cations was achieved. Therefore, the addition of crown ethers [1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6)] to the acidic eluent was carried out for the simultaneous separation of these mono- and divalent cations. Using 1.5 mmol dm^–3 oxalic acid–3 mmol dm^–3 15-crown-5 as the eluent, both highly sensitive detection and excellent simultaneous separation of these mono- and divalent cations were achieved in 10 min. The proposed IC method was successfully applied to the determination of major mono- and divalent cations in various natural water samples.