Retention behavior of common mono- and divalent cations on calcinated silica gel columns in ion chromatography with conductimetric detection and the use of nitric acid, containing crown ethers, as eluents

Ion chromatographic behavior of common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) on columns packed with silica gels (Super Micro Bead Silica Gel B-5, SMBSG B-5) calcinated at 200, 400, 600, 800 and 1000 °C for 5 h was investigated using nitric acid containing crown ethers [18-crown-6 (1,4,7,10,13,15-hexaoxacyclooctadecane) and 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane)] as eluent. When using 0.5 mM HNO3 as the eluent, the calcination had almost no effect on the improvement of peak resolution between these mono- and divalent cations. In contrast, when using 0.5 mM HNO3 containing crown ethers as the eluent, with increasing the calcinating temperature, the amount of crown ethers adsorbed on the corresponding calcinated SMBSG B-5 silica gels columns increased and, as a consequence, peak resolution between these mono- and divalent cations was quite improved. Excellent simultaneous separation of these mono- and divalent cations was achieved on column (150×4.6 mm I.D.) packed with the SMBSG B-5 silica gel calcinated at 1000 °C by elution with 0.5 mM HNO3 containing either 1.0 mM 18-crown-6 or 5.0 mM 15-crown-5.