Red residue in serum fatty acid analysis- extraction query!!

[ali4683]

I realise this issue is regarding the preparation of samples for GC analysis rather than the GC itself, but perhaps someone out there can help.

I'm currently extracting total fatty acids from human serum using the traditional folch method. Near the end of the procedure, following esterification with BF3 I reconstitute my samples in hexane and water, vortex and remove the top layer to dry under nitrogen. In about 60% of samples, there will be a red solid residue following drying down- this has only happened since I've been analysing serum samples and does not happen in all samples consistently. It will often happen to one control, but not the other.
Has anyone any ideas as to what could cause a red residue? I'm beginning to think it could be the nitrogen drying- has anyone come across a residue after drying before?

Thanks. Alison

[rpanetta]

Hi Alison,
I have seen something similar before and later found it to be due to old reagent. We also assumed it to be from drying, but multiple "blank" drying runs (i.e., just hexane in a vial) never gave us the residue. Once we shifted to a new batch of BF3/MeOH, the problem ceased.
Cheers!
Robert

[ali4683]

Robert thank you for your help. I have opened a new bottle of BF3 today and will keep my fingers crossed that this works!