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Sample Preparation - Quantifying silicon in silicone oil by ICP-OES

 
I have tried to quantify silicon in silicone oil by ICP-OES. To reach sample digestion, the mixture HNO3 (4 mL) + H2O2 (2mL) +HF (1mL) is used. Digestion is microwave assisted. Sample weight is 100 mg where only 3% is silicone oil, 97% is polymer. In spite of getting clear samples, silicon results are lower than real values. I've browsed on http://www.inorganicventures.com/elements/silicon and found a suggestion to digest silicone oil with conc. H2SO4/H2O2 followed by cooling and dissolution of the dehydrated silica with HF. May I perform this task using a microwave? Are there special quantities and procedures, or any alternative methods other than microwave digestion?
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admin Total posts: 529

If you perform a KOH digestion the details are as follows: use a clean LDPE bottle (HDPE has some Si) and mix the sample with the alcoholic KOH, where the KOH concentration in alcohol (ethanol or methanol) should be 0.5 - 1 M. Mix equal portions of the sample and alcoholic KOH and the temperature of digestion should be 60 degrees C (using a water bath is a good idea). Dilute the samples (and standards) in xylene or 2-butoxyethanol for the ICP-OES analysis.

Posted: 09/06/18 21:41:46
admin Total posts: 529

Our experience with silicone oils is primarily with direct analysis after pretreating the sample with alcoholic KOH to destroy volatile oligomers. I believe that your digestion procedure can be performed using your first approach but should incorporate a closed vessel digestion. I would like to suggest that you contact the microwave manufacturer concerning the possibility of using sulfuric and peroxide or the issue with your current method.

Posted: 09/06/18 21:41:01

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