Sample Preparation - Analyzing silicone oils
We are measuring silicone oil extracts of hair swatches on an AA. The 1% silicon oil standard we're using is in a MIBK/toluene solvent, but the mineral oil is interfering with the MIBK/toluene matrix. Do you have any recommendations?
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Silicone oils are difficult to analyze because they contain light oligomers with significant vapor pressures at room temperature. These give higher signals than a solid or high boiling liquid (e.g., vaporization interference). For sample preparation of silicone oils, the following information is from the Interactive Periodic Table on our website (http://inorganicventures.com/periodic-table): dimethyl silicones depolymerize to form volatile monomer units when heated (measure directly in an alcoholic KOH/xylene mixture where the sample is treated first with the KOH at 60-100 °C to "unzip" the Si-O-Si polymeric structure or digest with conc. H2SO4 / H2O2 followed by cooling and dissolution of the dehydrated silica with HF). Note that the direct analysis of silicone oils in an organic solvent will result in false high results due to high vapor pressure of volatile monomer units such as hexamethylcyclotrisiloxane. The KOH forms a nonvolatile silicone salt.The best solvent to use is xylene. If you choose not to use the KOH preparation technique, have your standard be the same viscosity of silicone oil as is being analyzed and use xylene as your solvent. |