Simultaneous determination of silicon and phosphorus in soil and plants by reversed-phase ion-pair chromatography

A reversed-phase ion-pair high-performance liquid chromatographic method, using tetrabutylammonium bromide (TBABr) as ion-pair reagent, has been developed for the simultaneous analysis of silicon (Si) and phosphorus (P) as heteropoly acids in soil and plant samples. The effect of the concentrations of ion-pair reagent, acetate buffer and organic modifier as well as the pH of buffer on separation was made clear. The reaction conditions and stability of heteropoly acids were investigated. Furthermore, the phenomenon occurred in the optimized process was also further researched. The separation was performed on a reversed-phase C18 column within 11 min with 40:60 (v/v) 0.1 M acetate buffer (pH 3.9)–acetonitrile (ACN) containing 0.8 mM TBABr as a mobile phase. The linear ranges of the peak area calibration curves for Si and P were 0.08–50 mg/L and 0.40–50 mg/L, respectively. The detection limits calculated at S/N = 3 were 0.0057 mg/L and 0.0280 mg/L for Si and P, respectively. The method was successfully applied to the analysis of soluble and total contents of Si and P in soil and plant samples.