By Luc Wynants on Thursday, October 23, 2003 - 01:07 am:
I have a very weird problem. I work with an HP5890 GC coupled to a HP5972 MS. The conditions are
Col. CP-SIL 8, 30mx0.25mm ID
Injector. 250°C
T0 75°C, hold 3min, 20°C/min to 255°C
Detector 300°C
Flow 1ml/min
I have never had problems seeing phenols. Suddenly, I can not even see a peak at a 100mg/l concentrion, while my I.S. 2-fluorobiphenyl (50 mg/l) is perfect. I have tried a semi-volatile standard and the whole chromatogram is perfect at 20mg/l (although different program, but same column).
If I inject 1000mg/l of phenols, the peaks are there. It is as if the phenols just don't reach the column. I have replaced the septum, liner and the gold seal at the botom of the liner. I have tried the same with a new column on an FID, with the same (negative)result.
Can someone help me? Thanks in advance.
Luc
By Anonymous on Thursday, October 23, 2003 - 11:09 am:
I would suspect that there is something in your solvent or sample prep that contributes to the retention of the phenols.
Investigate where these phenols are going. They were injected, so where did they go? Is there something being injected with them that complexes the phenols, and that has a limited amount of capacity to react with phenols in solution?
By Anonymous on Thursday, October 23, 2003 - 12:08 pm:
Here we trimethylsilylate phenolic compunds for GC, to reduce reactivity in the inlet and improve reproducibility.
By luc.wynants@toxikon.be on Friday, October 24, 2003 - 12:34 am:
Thanks for the advise both "Anonymous". I have indeed changed from MeOH as solvent to CH2Cl2 and the results were better on the FID. Today I will test with the GC-MS. Next step will then also be to try and deritavise them.
I will post the results here in case someone else has encountered the same problem and would be following this conversation.
Thanks again.
Luc
By Anonymous on Friday, October 24, 2003 - 06:12 am:
I suspect that water in the methanol was your problem. I would only use hexane for phenol compounds, with dichloromethane as a possible substitute, but not preferred. I would also shoot derivitization reagent like DMCS or BSA though the injection port and column to neutralize any active sites before shooting underivitized phenols. You will see reversal of isomers after derivitization for some phenolic compounds.
Rod