Chromatography Forum

Dear all,

I'm Giacomo and I'm studying for the degree of environmental engineering in Brescia, Italy. I'm doing the thesis about the survey of pharmaceuticals with GC-MS, especially carbamazepine and diclofenac.
I would not use the LC-MS/MS; so the HPLC it's not so exact as I wish.
May I have a bit of advice about CBZ (please) like:

1) What kind of internal standard I have to use? What do you think about azobenzene? Moreover I wouldn't use 13C/15N-carbamazepine standard and standard deuteride because they are too much expensive.
2) How I can keep down or avoid (imino)stilbene formation? (a tempereture too near at the melting point, shift my issues).
3) I need some information to prepair samples (I want to avoid derivatization) and to establish the parameters of GC-MS.

Thank you for help.
I look forward to hearing from you.


P.S.: I'm really sorry for my English, I hope you'll be able to understand.

Thank you again.

Giacomo,

I would consider derivatization of these analytes. It is worth trying a sample on the column to see how they behave, but I would be concerned about degradation of these compunds - particularly as the GC system is used for a while and the inlet liner begins to gather residues from many injections (even if you change it frequently). I would be concerned that diclofenac would form the cyclic amide, for instance. I took a quick look for related literature online, and have found that both of these compunds have been analyzed by GC - with derivatization.

Make your internal standard as chemically similar to your analytes as possible. If your analyte is an ester or amide, pick an ester or amide. The idea is to be sure that losses and degradation of the internal standard should be a similar as possible to the analyte. (Not that one wants much in the way of loss or degradation in the first place.) You want the internal standard to elute close to your analytes in the chromatogram - if for no other reason that you can keep your runs as short as possible.

Hi

Agree with Don here.

carbamazepine (primary amine bp ~190°C) you most likely could do without dervatisation and with diazepame as internal standard. But as Don mentioned, then you would need to ensure that yout GC system is really inert so that the amine does not interact too much with active sites such as silnol groups.
As for diclofenac (secondary amine with a carboxylic acid side chain) I can not see that you can manage without dervitisation here, the link below mention a dervatisation step.


http://www.informaworld.com/smpp/conten ... order=page

Thank you very much

I've looked for carbamazepine derivatization in literature online but I just found some information about derivatization of diclofenac.
Can you suggest me some website where I can found what I'm looking for?

Many people advice me to use pyrene as internal standard. What do you think about it?
However, I'll try with diazepame.

I've already done some test with GC-MS about CBZ.
The most problem is the formation of iminostilbene; I think that is a consequence of high temperature of inlet system and because I hadn't used a new liner. With the new liner and not too high temperatures (210-220°C) it creates less iminostilbene, but for each test the iminostilbene/CBZ ratio is always different!
Now I'm going to try the test with a temperature of ~300°C, I hope that all carbamazepina will turn into iminostilmente.
Can this is a usefull test?


Thanks a lot,
I hope you'll be able to help me

I just did a Google search for carbamazepine and GC. Given that I am in a bit of a rush, I'll have to leave that to you to check out.