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EFFICIENT SOLID PHASE EXTRACTION PROCEDURES FOR ORGANO SILOXANES AND SILANOLS FROM AQUEOUS AND BIOLOGICAL MATRICES

Efficient solid phase extraction (SPE) procedures were established to extract a variety of organosiloxanes and organosilanols at low concentrations from aqueous and biological matrices. The organosilicon materials used in SPE experiments were all 14C-labeled. Use of 14C-labeled materials made it very convenient to determine the SPE process efficiency. For non-polar siloxanes of lower molecular weight, viz., 14C-octa-methyl-cyclotetrasiloxane (D4), 14C-decamethylcyclopenta-siloxane (D5), and 14C-hexamethyldisiloxane (MM), the recoveries from aqueous solutions, using C18 SPE cartridges, were 91 (± 2), 98.6 (± 0.5), and 96.2 (± 2), % respectively. For polymeric siloxane fluids of 350 and 1000 cSt viscosities with number average molecular weights, Mn of ∼9800 and 17,000 respectively, C4 sorbent was preferred. The recoveries for these polymeric siloxanes were 89.3 (± 1.7), and 96 (± 0), % respectively. For polar silanols, styryl-divinylbenzene based polymeric-sorbent ENV+® worked exceptionally well. Using ENV+ sorbent, samples of dimethylsilanediol Me2Si(OH)2, methylsilanetriol MeSi(OH)3, were recovered from aqueous medium with excellent efficiencies (99 and 94 %, respectively). The ENV+ cartridge was also applied to recover very efficiently the metabolites (i.e. hydroxy and hydroxymethyl functional siloxanes) of D4, D5, and MM present in rat urine. The recoveries were >90% in all cases. Recoveries of metabolites of MM and D5from plasma were ∼80 and 66% respectively. The concentrations of the analytes ranged from parts per billion to parts per million. For successful retention of the analytes to the sorbent, it was found to be necessary to place solid NaCl to the top of the SPE cartridge bed, or treat the aqueous matrices with NaCl prior to sample load. HPLC analyses of samples performed following the SPE process showed that the organosilicon materials, including the very reactive silanols, remained unchanged.