Trimethylsilylation of commonly occurring primary and secondary minerals in soils

Abstract

Soil is formed through the weathering of minerals-mainly silicates-and the manner in which these materials weather is related to some extent to the arrangement ofsilica units within their structures. This has been termed the degree ofpolymerizafion ofthe silica and can be quantitatively assessed by preparing organic (trimethylsilyl) derivatives which can be separated and identified. This procedure has been applied to a number of primary and secondary (including clay and highly disordered) minerals occurring in soils and has indicated that: (a) of the primary minerals, the ferromagnesian are the most susceptible to acid attack; (b) inorganic gels, particularly those high in alumina, are reactive; and (c) crystalline clay minerals, especially kaolinite and illite, are relatively stable.

Characterization of X-ray amorphous material in a Scottish soil by selective chemical techniques

“…The methods used in this investigation involved dissolution by alkali (Follett et aL, 1965), dithionite (Mitchell et aL, 1971), acid oxalate (Smith, 1984) and pyrophosphate (McKeague, 1967), trimethylsilylation (Smith et al, 1982) and fluoride exchange (Perrott et al, 1976).…”

“…The method was used initially in structural studies of crystalline silicates, glass and cement (Lentz, 1966;Gotz & Masson, 1971). Recently it has been applied to investigation of soil minerals, both clay and accessory minerals, where it has proved particularly valuable in the characterization of aluminosilicate gel material (Smith et at., 1982). The results obtained for the Tom Na Gabhar soil profile (Table 5) indicate a gradual decrease in the amount of aluminosilicate gel material with depth.…”

Susceptibility to weathering of some Scottish rocks and their derived soils

“…The stability of the samples to acid was assessed from the amount of monomeric silica released during trimethylsilylation by the method of Smith et al (1982), which involves treatment with trimethylchlorosilane in the presence of a small amount of water. The hydrochloric acid produced leaches the silicate minerals, replacing cations with protons, and the silicic acids so released immediately form derivatives with trimethylsilyl (TMS) groups.…”

“…Since this technique involves determination of the amount and course of dissolution incurred by silicates during prolonged and controlled acid attack, it seemed promising for providing information on the stability of specific species in an acidic environment. Application to silicate minerals ranging in structure from highly ordered to highly disordered (Smith et al 1982) revealed (a) that the amount of monomeric silica released was generally greater than that of dimeric, which in turn was greater than the amount of higher polymeric forms (trimer ring, tetramer ring, trimer chain), (b) that ferromagnesian minerals were particularly susceptible to acid attack, (c) that inorganic gels, particularly those high in alumina, were fairly readily attacked and (d) that crystalline clay minerals, particularly kaolinite and illite, were relatively resistant. Some values relevant to the present investigation are listed in Table 4.…”

“…In the first group, the relatively large amounts of monomeric silica produced by the C and D horizons of the gabbro soil probably result from the inorganic gel and ferromagnesian minerals present (Table 4; Fig. 4a), whereas the higher values in the A and B horizons presumably Table 4 Relative amounts of silica as monomer and dimer (mg/g) obtained on trimethylsilylation of natural and synthetic mineral materials (Smith et al 1982 247-0 207-0 161-0 16-2 9-1 8-4 8-2 2-6 2.0 1-9 1-9 0-8 0-7 0-7 0-6 0-4 0-3 0-1 <0-05 Monomer 2-4 2-0 1-9 1-5 1-3 1-0 0-6 0-3 117-0 72-2 59-3 57-9 37-9 24-6 22-7 8-9 2-4…”