Microwave Digestion for Colorimetric Determination of Total Si in Plant and Mineral Samples

ABSTRACT

A new method for determining the soluble silicon (Si) concentrations in nonliquid plant and mineral samples was developed using sodium hydroxide (NaOH)–hydrogen peroxide (H₂O₂) matrix for microwave digestion (MWD-Na) followed by colorimetric Si testing. MWD-Na was compared with autoclave-induced digestion and alkali fusion. The data have shown no significant difference between these three methods. HNO₃–H₂O₂ or HNO₃​–H₂O₂​–HF microwave technique results in Si loss. The reduction of the total Si can be realized via low solubility of Si in the acid solutions or silicon tetrafluoride formation. The Mullen and Riley method for colorimetric testing of Si in a solution that uses ascorbic acid to reduce the silicomolybdate complex formed under acid conditions to an intensely blue complex was modified using iron sulfate. The combination of MWD-Na and modified colorimetric blue method provides cheap and valid data on determining the total Si in both plant and mineral samples.

KEYWORDS:

• Alkali fusion
• autoclave digestion
• microwave digestion
• plant sample digestion
• silicon

Additional information

Funding

The study was supported by the National Key Research projects, Ministry of Science and Technology of China (project number: 2016YFD0800705) and by the National Science Foundation of Hunan Provincial (project numbers: 2016JJ6066, 2017JJ3161).