Method tips?

[DeniseHeinz]

Hi,

I'm working on a method for a completion of reaction. My starting material is a long chain, saturated fatty acid and it's converted to the corresponding alcohol. Since it is semi-volatile, I was thinking of adding a silylation derivatization as that seems pretty easy to do. I wrote restek about this and they suggested using a FAME column. Initial work will be on a GCMS and later on moving to FID. Any thoughts on a good column or procedure to use?

thanks,
Denise

[Consumer Products Guy]

So you may have both long-chain fatty acids and fatty alcohols both? The trimethylsilation should be fine. Take up your sample in solvent like DMF and mix with silylation agent such as BSTFA and inject. I'd recommend a nonpolar capillary like DB-5, FAME columns are most often used for fatty acid methyl esters, to separate the saturated methyl esters from the saturated ones.

We routinely assay fatty alcohols and fatty alcohol ethoxylates (nonionic surfactants) using trimethylsilylation here.

[Peter Apps]

For the sake of simplicity I would go with a PEG wax type column and analyse the mixture as is - no derivatization. Modern columns are very well deactivated so tailing should not be a problem.

Peter

[DeniseHeinz]

To Consumer Products Guy:
Yes, both the fatty acid and fatty alcohol will be in the same sample. And, lucky for me, we already have a DB-5 installed on the GC-MS.

Also, do you normally evaluate different conditions for the TMS derivatization? I have a protocol that I was using for sugars (Sweeny, 1965) and I was going to try that out first.

Here's what I was using:
Sample Preparation
A) 10mg of sugar was weighed into a micro-centrifuge tube. To the tube, 1mL of anhydrous pyridine was added. The vial was swirled to dissolve the sugar. To the tube, 0.2mL of hexamethyldisilazane and 0.1mL of trimethylchlorosilane were added. The tube was capped and shaken for 30 seconds. The tube was briefly centrifuged to allow solids to settle on the bottom.

[DeniseHeinz]

Hi Peter,

We've also talked about shooting it w/o derivatizing, but I wasn't sure if the C20+ fatty alcohols would have problems. I'll try your suggestion out too.

Thanks!