Stupid mistake in GC-MS?
Posted: Tue Jun 26, 2007 12:13 pm
Hello!
I have developed a new method for hormone analysis with GC-MS. The hormones are extracted (from water) in 10 microL of di-n-hexylether (b.p. 220) containing 10% tri-octyl-phosphine oxide (bp 202). I derivatized with MSTFA (20 microlitres) and then injected. I finished the method development which resulted in good results. However, since last method optimization experiment I have problems with the chromatogram. That time I had to run 2 times the samples because the first time I did not get any resolved peak (the backgrouwnd is quite flat instead of having different peaks). At the beginning I thought it had something to do with the injection because the first injection did have more resolved chromatogram. (I did change from automatic to manual injection, increased the injection temperature, change the gradient a little etc), but nothing really changed. In the last run I did only manage to get one good chromatogram out of 18 injections. The last thing I have done is to derivatized 2 hormones in pure di-n-hexyl ether (DHE), DHE containing 5% and 10% Trioctylphosphine. The chromatography became worst with the trioctylphosphine addition, the more the worst.
So my question is: did I make a stupid choice when using trioctylphosphine? Is there any reason why I should not use it in MS? Why did it work at the beginning (or sometimes) and not now?
Thank you very much for your help.
Saioa
I have developed a new method for hormone analysis with GC-MS. The hormones are extracted (from water) in 10 microL of di-n-hexylether (b.p. 220) containing 10% tri-octyl-phosphine oxide (bp 202). I derivatized with MSTFA (20 microlitres) and then injected. I finished the method development which resulted in good results. However, since last method optimization experiment I have problems with the chromatogram. That time I had to run 2 times the samples because the first time I did not get any resolved peak (the backgrouwnd is quite flat instead of having different peaks). At the beginning I thought it had something to do with the injection because the first injection did have more resolved chromatogram. (I did change from automatic to manual injection, increased the injection temperature, change the gradient a little etc), but nothing really changed. In the last run I did only manage to get one good chromatogram out of 18 injections. The last thing I have done is to derivatized 2 hormones in pure di-n-hexyl ether (DHE), DHE containing 5% and 10% Trioctylphosphine. The chromatography became worst with the trioctylphosphine addition, the more the worst.
So my question is: did I make a stupid choice when using trioctylphosphine? Is there any reason why I should not use it in MS? Why did it work at the beginning (or sometimes) and not now?
Thank you very much for your help.
Saioa