BHA and BHT via GC

[MSCHemist]

Does anyone have a good method protocol for doing BHA BHT in edible oils via GC. I am having trouble getting decent recovery especially of BHT. I am dissolving in Pet ether and extracting with acetonitrile but need to do at least 3 extraction to get full recovery of BHT using up a lot of solvent and I don't have a turbovap here to blow it down.

[KM-USA]

See Quantitative determination of BHT in soap products by capillary gas chromatography, » Journal of the American Oil Chemists Society
» Volume 59, Issue 12 , pp 579-582

Works for BHA too, and in fatty acids, fats and oil as well. You won't have the fragrance interferences they had with finished bar soaps.

[MSCHemist]

Thanks for the reference but I decided to just dilute the oil .1g to 100ml with ethanol and even at 50:1 I have enough sensitivty for either Scan or SIM but I decided on SIM (why not the S/N is great).

[MSCHemist]

One of the issues that just came up is I am able to resolve 2-BHA from 3-BHA. My samples contain ~5% 2-BHA but my refernce standards are all 3-BHA. I quant off the 165 m/z ion which is the base ion for both 2 and 3-BHA but I am concerned the response factors are a bit different so I am hesitant to just add the 2-BHA area to the 3-BHA.

[MSCHemist]

Looks like I am almost there. My samples are based in soybean oil the antioxidant is ~20%BHA and 20%BHT and the finished product about 1% BHA and 1% BHT. I started the validation. I am diluting the antioxidant 20000 fold in 96% ethanol (from the liquor store) with di-BHA ITSD and the finished product 1000 fold and doing it in SIM mode with a single quant ion 50:1 split with calibration points at 1, 5, 10, and 25ppm. I am just adding the 2-BHA to the 3-BHA area count.

My recoveries in artificial samples (BHA and BHT dissolved in soybean oil) are 95-105% and the precision is ~2%RSD

There still seems to be a bias about 5-7% low compared to the parent company lab and supplier's COA which use HPLC-DAD.