Try this:
Extraction of tissue and feedingstuff:
Weigh 2g of homogenized sample into a 50mL centrifuge tube (add standard/internal standard solution add allow sit for 30 min).
Add 5mL MeOH and extract the sample for 10 min in an ultrasonic bath, vortex for >1 min, centrifuge the sample for 10 min (3500×g) and transfer the supernatant to a 10mL tube.
Repeat the extraction step with an additional 5mL MeOH and add to the same 10mL tube.
Evaporate the sample to 100-200uL under a gentle stream of nitrogen.
Redissolve the sample in 1mL of dichloromethane–cyclohexane (1:1).
Clean-up:
The reconstituted extracts are cleaned-up with silica cartridges (500 mg /6 mL, P/N: CUSIL156).
If residual water is an issue in the reconstituted sample and affects the SPE step, sodium sulphate can be added to the silica cartridge. But hopefully this won't be necessary.
Condition the silica SPE cartridges with 10mL of cyclohexane before loading the extracts.
Load the sample and allow to pass through dropwise without vacuum.
Rinse the sample tube with an additional 0.5 mL of dichloromethane–cyclohexane (1:1) and add to the SPE cartridge.
Rinse the cartridge with 5mL of cyclohexane to remove matrix interferences.
Elution is carried out with 5mL of a 40:60 mixture of cyclohexane-ethyl acetate.
Evaporate the sample to dryness under a gentle stream of nitrogen.
To derivatize the thyreostats add 100 µL of MSTFA (or an alternative derivatizing reagent to the tube, vortex briefly and heat the sample at 55°C for 30 min.
After derivatization, bring the final volume to 1mL with acetone, vortex thoroughly and transfer the sample to an autosampler vial for GC-MS analysis.
