Quantitative Determination of Octamethylcyclotetrasiloxane (D4) in Extracts of Biological Matrices by Gas Chromatography-Mass Spectrometry

Abstract

A method was developed and validated to measure octamethylcyclotetrasiloxane (D₄)^? quantitatively by gas chromatography-mass spectrometry (GC-MS) at low level in extracts of several biological matrices that include plasma, liver, lung, feces and fat from rats. The key to the successful determination lay in the use of extracts dried with anhydrous magnesium sulfate. This was necessary in view of the propensity of the methyl siloxane based GC-stationary phase to generate D₄ by its reaction with water present in the extracts. To enable quantiiation of D₄ at parts per billion (μg/L) levels, the base ion m/z 281 resulting from the loss of a methyl group from the parent molecule was selected for monitoring by SIM mode in GC-MS. The recovery of D₄ from any of the biological matrices was determined to be greater than 90% in three extractions. The D₄ response for the standards in GC-MS was linear (R² > 0.9900) and reproducible at concentrations ranging from 1—16,000 ng D₄/g solvent. Precision was less than 5%.     

Heterocyclic synthesis via thallation and subsequent palladium-promoted olefination

The thallation and subsequent palladium-promoted olefination of p-tolylacetic acid, N-methylbenzamide, benzamide and acetanilide provides a novel new route to a variety of important oxygen and nitrogen heterocycles.     

A Primer on the Analytical Aspects of Silicones at Trace Levels-Challenges and Artifacts – A Review

Silicones (polydimethylsiloxanes) find use in a wide variety of industrial and consumer product applications because of their outstanding properties. Potential human exposure to silicones occurs at the work place during manufacturing and product formulation, as well as through the normal use of consumer products containing them.The entry of silicones into various environmental compartments raised health and safety concerns from potential exposure and mandated numerous environmental and toxicological studies. Such studies require qualitative and quantitative determination of silicone species at trace levels. However, the ubiquitous presence of silicones coupled with their unique chemistry renders their analysis at trace levels challenging.This paper provides a consolidated account of various aspects silicones that must be borne in mind to obtain reliable data. The following are some of topics discussed: differences in the chemistry of silicones vs carbon; precautions in sample handling to avoid losses and inadvertent chemical transformation; potential sources for artifacts and interferences that could lead to systematic errors and data misinterpretation; sources for background and the need for matrix matched blank experiments; distinguishing silicones from silicates to avoid overestimation; potential for incorrect structural assignments; preventing inadvertent contamination; questionable claims on the presence of silicones in biological matrices including that of silicone implants.     

Utility of trichloroisocyanuric acid in the efficient chlorination of silicon hydrides

The potential of trichloroisocyanuric acid (TCCA) as a chlorination agent for efficient conversion of Si-H functional silanes and siloxanes to the corresponding Si-Cl functional moieties was explored. In comparison to methods using other chlorinating agents, TCCA is inexpensive, results in a much faster reaction and produces a high purity product with a conversion that is essentially quantitative. A variety of chloro derivatives of linear and cyclic structures have been synthesized from silicon hydrides using this reagent with impressive yields that typically exceed 90%: PhSiCl₃ (97.5%); PhMeSiCl₂ (95.5%); Ph₃SiCl (97.5%); Vi₃SiCl (98.7%); (EtO)₃SiCl (99.7%); t-Bu₃SiCl (∼100%); (MeClSiO)₄ (86.5%); (MeClSiO)₅ (95%); (MeClSiO)₇ (96.5%); Ph(OEt)₂SiCl (98%); ClMe₂SiOSiMe₂Cl (98.6%); ClMe₂SiOSiMeClOSiMe₂Cl (94.6%); ClMe₂Si(OSiMeCl)₂OSiMe₂C l (92.3%); (Me₃SiO)₃SiCl (97%); Me₃SiOSiClPhOSiMe₃ (99%); Me₃SiO(SiMeClO)₃SiMe₃ (95.7%); ClSi(OSiMe₃)₂OSi(OSiMe₃) ₂Cl (93.6%).For monohydridosilanes, dichloromethane (CH₂Cl₂) was a suitable solvent in which nearly quantitative conversion was observed within several minutes following the addition of the silanes to TCCA. For certain cyclic and linear siloxanes, and especially silanes containing multiple hydrogen atoms on the same silicon for which the reaction is sluggish in CH₂Cl₂, tetrahydrofuran (THF) was the preferred solvent. For a sterically demanding silane that did not undergo chlorination even in THF viz., HSi(OSiMe₃)₂O-Si(OSiMe₃)₂H, 1,2-dichloroethane was the best solvent.