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- Posts: 12
- Joined: Tue Nov 16, 2004 8:04 pm
I have been analyzing derivatized bile acids- cholic acid, doexycholic acid, lithocholic acid - by GCMS with variable success. I have tried derivatizing the acids with 9:3:1 Pyridine:HMDS:TMCS, and 3:1 HMDS:TMCS, as described in the many literature references I have found, most of them around 40years old.
The technique seems to work well, but the resulting derivatives appear to be very unstable to moisture or lower alcohols such as methanol. I have done some work making methyl esters of acids, which is also supposed to be moisture sensitive, but this is a completely different ball game. Just transferring the samples from sealed reaction vials to autosampler vials is often enough to destroy my derivatives.
So my questions are this:
Am I doing something wrong, is it possible to produce a more stable derivative?
Some of the literature I've seen talk about first forming methyl esters, then further derivatizing to Trimethylsilyl ethers, am I leaving out an important step if I go straight to the TMS derivatives?
Any help would be greatly appreciated.
Mike
The technique seems to work well, but the resulting derivatives appear to be very unstable to moisture or lower alcohols such as methanol. I have done some work making methyl esters of acids, which is also supposed to be moisture sensitive, but this is a completely different ball game. Just transferring the samples from sealed reaction vials to autosampler vials is often enough to destroy my derivatives.
So my questions are this:
Am I doing something wrong, is it possible to produce a more stable derivative?
Some of the literature I've seen talk about first forming methyl esters, then further derivatizing to Trimethylsilyl ethers, am I leaving out an important step if I go straight to the TMS derivatives?
Any help would be greatly appreciated.
Mike
