11.2. TOTAL ANALYSIS
11.2.1. Gravimetric methods.
The earliest procedures used to analyze various materials for Si were based on gravimetric methods utilizing chemistry that produced either losses or increases in weight. Typical weight loss methods utilize HF to evolve Si as SiF4 gas. Robinson (1945) used this principle to analyze for Si in soils, after first bringing Si into solution by fusion. For determining Si in an organic matrix, such as plant tissue, the organic matter can be removed by oxidation at 550 C. After solubilizing non-Si elements in 6M HC1, the sample is filtered through ashless paper that retains the Si precipitate. The paper is ignited and weighed. Then HF is used to evolve the
Si, so that the weight loss is assumed to be Si.