Extraction of octamethylcyclotetrasiloxane and its metabolites from biological matrices

Octamethylcyclotetrasiloxane (D4) is an industrial chemical of significant commercial importance. It is a key ingredient in a variety of product formulations and a critical intermediate in the production of silicone polymers. As part of the pharmacokinetic investigation of its disposition and metabolism, an efficient extraction methodology has been developed to recover both the parent D4 and its metabolites from various biological matrices, including blood, plasma, urine, feces, liver, lung, and fat. Of the common organic solvents evaluated (hexane, methylene chloride, diethylether, chloroform, methylisobutylketone, etc.), tetrahydrofuran (THF) was demonstrated to be an excellent choice for extracting both D4 and its metabolites. Test samples were either spiked with 14C-D4 or obtained from animals administered 14C-D4 via various exposure routes (inhalation, i.v., etc.) and then subjected to THF extraction. Recoveries of D4 and its unbound metabolites from plasma were essentially quantitative in three extractions. Even in a single extraction, the recoveries were > 90%. Similar results were obtained for other matrices as well. Extraction efficiencies were measured as follows: lung, 98.2 +/- 0.3%; liver, 95.4 +/- 0.4%; fat, 99.4 +/- 0.8%; urine, 98.1 +/- 0.2%; feces, 94.1 +/- 0.6%. HPLC profiles obtained before and after extraction were essentially identical, further confirming the suitability of THF as an extractant.