STUDIES ON THE OPTIMUM CONDITIONS OF EXTRACTION OF SILICON SPECIES FROM PLANTS WITH WATER – III.¹ On the Stability of Silicon Species in Extracts from Equisetum arvense Herb

Abstract

The stability has been studied of molybdate-reactive silicon species in aqueous extracts from Equisetum arvense herb of various concentrations, both pure and preserved with formic acid, sorbic acid, sodium benzoate and ethyl p-hydroxybenzoate. The level of the silicon species in the extracts was much higher than that corresponding to a stable aqueous solution of orthosilicic acid (56 mg Si/dm³). Pure extracts, containing 170 mg Si/dm³ were stable for prolonged periods. Concentrated ones, preserved with 0.01 % of formic or sorbic acid, showed excellent stability over the whole period studied (9 days) with molybdate-reactive silicon level ranging from 300 to 380 mg Si/dm^s. The acidity of the extracts along with the protective action of organic matter have been found to be essential for ensuring enhanced stability as compared with that of aqueous solutions of orthosilicic acid.