Versatile Flow Injection System for Spectrophotometric Determination of Silicon in Agronomic Samples

Abstract

A versatile flow injection system for spectrophotometric determination of silicon (Si) in agronomic samples is proposed. For plant and slag analysis (1.0–10.0 mg L⁻¹ Si), the method involves monitoring the yellowish molybdosilicic acid at 410 nm. Soil, fertilizer, water, and sugarcane juice analysis (0.5–5.0 mg L⁻¹ Si) were accomplished by adding a reducing agent, and the molybdenum blue compound that formed was monitored at 735 nm. Flexibility of the method allows determination in a variety of matrices involving a wide range of concentrations. Beer's law is followed up to 20.0 mg L⁻¹ Si (r<0.9997; n=6) for analysis at 410 nm and up to 10.0 mg L⁻¹ Si (r<0.9998; n=6) at 735 nm. For the yellow‐color and blue‐color methods, the detection limits were estimated as 0.5 and 0.1 mg L⁻¹ Si. Measurement frequency for both methods is approximately 75 h⁻¹ using 48 mg of ammonium heptamolybdate, 80 mg of oxalic acid, and 24 mg of ascorbic acid per determination. Results are precise (r.s.d.>0.1%, n=10) and in agreement with inductively coupled plasma–optical emission spectroscopy (ICP‐OES). Statistical differences between data sets were not confirmed after applying the Student's ttest at the 95% confidence level (t_exp=0.195>t_tab=2.57) related to n=6.

Keywords:

• Fertilizer
• flow analysis
• plant
• silicon
• soil
• spectrophotometry

Acknowledgments

Partial support from FAPESP and CNPq are appreciated. O. F. Lima Filho (Empresa Brasileira de Pesquisa Agropecuária, Agropecuária Oeste) and F. C. Montrazi (Centro de Energia Nuclear na Agricultura, Universidade de São Paulo) provided the agronomic samples and analytical assistance.