A new sample preparation procedure for the determination of Si in plant materials by ICP OES is proposed. A two-step digestion procedure employing diluted solutions of HNO3 (1.0 mol L−1) and NaOH (1.5 mol L−1) was applied for digesting plant samples. Limits of detection and quantification for Si were 56 and 186 μg g−1, respectively. A comparative study was done to evaluate the accuracy of the developed procedure by comparing the results obtained for Si in five sugar cane leaf samples with those obtained by micro-energy dispersive X-ray fluorescence (μED-XRF) and according to a t-test the results agreed at the 95% confidence level. To verify the versatility of the procedure, Si, Al, B, Ca, Cu, Fe, K, Mg, Mn, Mo, S, and Zn were simultaneously determined in plant materials. The analytes were quantified in four certified reference materials: apple leaves (NIST 1515), tomato leaves (NIST 1573), white cabbage powder (BCR-679), and bush branches and leaves (NCS DC 73349) for accuracy assessment. All recoveries were in the range of 91.0–109% and all results agreed at the 95% confidence level (t-test) with certified concentrations. Foliar diagnosis was performed to demonstrate the applicability of the developed procedure for leaves of sugar cane, corn, soy and alfalfa. The proposed procedure is simple, versatile, reliable and safe for the determination of Si, macro- and micro-nutrients in plants by ICP OES.
