Esterification of short chain acids

[scottjn]

Hello,

I am trying to do a chiral GC analysis of a short chain hydroxy acid. I can only get separation when I make the methyl ester. I am using TMS-diazomethane but there are so many background peaks that the analysis is nearly impossible. The GC temp program is at a somewhat low temp and this is, I believe, one reason why there are so many garbage peaks.

Can someone recommend another esterificaiton method that may give less background peaks? I'm only looking to calculate e.e. so it doesn't need to be quantitative.

Thanks!

[Bruce Hamilton]

A lot of recent work has been performed using direct injection into suitable columns, such as Nukol and Vocol ( supelco? ) columns.

There is ahuge amount of literature on techniques in the J. food Scioence and other aroma journals.

I suspect your problem is the derivatisation reagents. I've always used generation of DAM as required, rather than solutions because of the known amounts of artifacts that appear. I try to avoid TMS for the same reason.

As usual, I would always start with W.W.Christie's WWW site when looks for chromatographic analysis of lipids and fatty acids.
http://www.lipidlibrary.co.uk/index.html

If you don't have access to a good library, a Google search for " Volatile hydroxy acids GC " should also find some useful older papers.

Bruce Hamilton

[scottjn]

Thanks Bruce. I'm actually trying to do a chiral separation, so those columns would not work in my case. DAM may work, but because of the safety issues, it may take too long to implement. Thanks.

A lot of recent work has been performed using direct injection into suitable columns, such as Nukol and Vocol ( supelco? ) columns.

There is ahuge amount of literature on techniques in the J. food Scioence and other aroma journals.

I suspect your problem is the derivatisation reagents. I've always used generation of DAM as required, rather than solutions because of the known amounts of artifacts that appear. I try to avoid TMS for the same reason.

As usual, I would always start with W.W.Christie's WWW site when looks for chromatographic analysis of lipids and fatty acids.
http://www.lipidlibrary.co.uk/index.html

If you don't have access to a good library, a Google search for " Volatile hydroxy acids GC " should also find some useful older papers.

Bruce Hamilton

[Tony]

Acid methylation will work - i.e. 1NHCl in MeOH with sample heated to 85degreesC for a couple of hours. This method is generally not mentioned in the literature/brochures for FAMES < C8 because they are so volatile. But if you methylate in a closed vial, then cool in the fridge/freezer before opening and partioning into hexane against a salt solution, you'll be fine. We've easily gone down to C3 FAMEs with this technique, with very clean backgrounds.


cheers
Tony

[Tony]

Acid methylation will work - i.e. 1NHCl in MeOH with sample heated to 85degreesC for a couple of hours. This method is generally not mentioned in the literature/brochures for FAMES < C8 because they are so volatile. But if you methylate in a closed vial, then cool in the fridge/freezer before opening and partioning into hexane against a salt solution, you'll be fine. We've easily gone down to C3 FAMEs with this technique, with very clean backgrounds.


cheers
Tony

[scottjn]

Great, thanks Tony.

Acid methylation will work - i.e. 1NHCl in MeOH with sample heated to 85degreesC for a couple of hours. This method is generally not mentioned in the literature/brochures for FAMES < C8 because they are so volatile. But if you methylate in a closed vial, then cool in the fridge/freezer before opening and partioning into hexane against a salt solution, you'll be fine. We've easily gone down to C3 FAMEs with this technique, with very clean backgrounds.


cheers
Tony

[Bruce Hamilton]

Just be wary of partitioning losses with short chain hydroxy esters. Recovery from a single partition, even with salt, may be quite low, and you may need multiple extractions.

Bruce Hamilton.