Simultaneous separation of common mono- and divalent cations by ion chromatography with indirect photometric detection using an unmodified silica gel column and tyramine–oxalic acid–15-crown-5 as eluent

Abstract

The application of an unmodified silica gel (Zorbax BP-SIL) column (150 × 4.6 mm id) to ion chromatography with indirect photometric detection (IC-IPD) using 4-aminoethylphenol (tyramine) as the eluent was carried out for the simultaneous separation of common mono- and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). By using 1 mmol dm⁻³ tyramine–0.2 mmol dm⁻³ oxalic acid at pH 4.75 as the eluent, complete separation of the divalent cations and incomplete separation of the monovalent cations were achieved in 12 min. Hence, the addition of 1,4,7,10,13-pentaoxacyclopentadecane (15-crown-5) to the eluent was carried out. By using 1 mmol dm⁻³ tyramine–0.2 mmol dm⁻³ oxalic acid–20 mmol dm⁻³ 15-crown-5 at pH 4.75 as the eluent, highly sensitive indirect UV photometric detection at 265 nm and excellent simultaneous separation of the mono- and divalent cations were achieved in 17 min. The proposed IC-IPD method was successfully applied to the determination of major mono- and divalent cations in natural water samples.