Separation of common monovalent and divalent cations by ion chromatography on calcined silica gel cation-exchange stationary phases, with tyramine-oxalic acid-containing crown ether mobile phases and indirect photometric detection.

Pure silica gels (Pia Seed 5S-60-SIL) calcined at 200, 400, 600, 800 and 1000°C for 5 h have been used as cation-exchange stationary phases in ion chromatography with indirect photometric detection for common monovalent and divalent cations (Li⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺ and Ca²⁺); 0.75 mm tyramine (4-(2-aminoethyl)phenol)-0.25 mm oxalic acid, pH 5.0, containing crown ethers (18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) or 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)) was used as mobile phase. With increasing calcination temperature, the amounts of the crown ethers adsorbed on the calcined silica gel column increased and, consequently, the effect of the crown ethers as retention modifiers for these cations increased. Excellent simultaneous separation and highly sensitive detection of these cations at 275 nm were achieved in 17 min by use of a 150 mm×4.6 mm i.d. column packed with silica gel calcined at 1000°C and use of 0.75 mm tyramine-0.25 mm oxalic acid, pH 5.0, containing either 0.5 mm 18-crown-6 or 5.0 mm 15-crown-5 as mobile phase. [ABSTRACT FROM AUTHOR]