Simultaneous determination of silicic acid, Ca, Mg and Al in mineral water and composite tablets by Ion chromatography

Summary

A simple, selective and sensitive ion-chromatography method was investigated for simultaneously determining silicic acid, Ca²⁺, Mg²⁺, Al³⁺ and anions (Cl⁻ and NO ⁻₃ ) in real samples. It involved a single-column ion-chromatograph with sodium hydroxide-methanol-water eluent and conductometric detection. Cations were converted to complex anions by adding EDTA to the sample solution. A set of well-defined peaks of silicic acid, Ca²⁺, Mg²⁺, Al³⁺, Cl⁻ and NO ⁻₃ were obtained. Detection limits using 3.3σ (σ=standard deviation of blank solution) were 1.25×10⁻⁶ M for H₃SiO ⁻₄ , 1.32×10⁻⁶ M for Ca²⁺, 1.28×10⁻⁶ M for Mg²⁺, 1.33×10⁻⁶ M for Al³⁺, 1.31×10⁻⁶ M for Cl⁻ and 1.24×10⁻⁶ M for NO ⁻₃ . The method was successfully applied to analysis of mineral water and composite tablets.