By Anonymous on Tuesday, January 21, 2003 - 08:06 pm:
The following situation was encountered:
Repeated injections of the same sample vial gave significantly different areas for the main component as well as for the solvent. However, the minor impurities always had similar areas. Therefore, it was impossible to tell the "real" %a/a of the impurites. (These impurities were not present in the blank injection.) What are the possible problems? I appreciate any suggestions/help. Thank you.
By Anonymous on Wednesday, January 22, 2003 - 06:15 am:
What are your analytes and run conditions? What are the impurities?
By Rodney on Wednesday, January 22, 2003 - 09:11 am:
I suspect that the detector was overloaded and you are not integrating the major peaks correctly or reproducibly.
That does not mean the impurities peaks are incorrectly integrated. You should quanitate with an external std to quanitate these peaks, and not by area percent.
Rodney George
Supelco
By Anonymous on Wednesday, January 22, 2003 - 10:31 am:
Thank you both for your quick responses suggestions. We are analysing carbazates and piperidine derivatives. The impurities are unidentified yet. This morning we have used the same column on another system and it worked fine. Then we need to verify the first system. One observation is that the head pressure sometimes had difficulties to stabilize. I don't know if this is related.
Thanks again.
Jan
By Anonymous on Thursday, January 23, 2003 - 07:59 am:
If the GC had trouble stabilizing the column head pressure it possibly has a small leak upstream of the column. This could cause varying results in the chromatogram, although I would have expected the impurities to vary also.
Regards,
Mark
By Anonymous on Thursday, January 23, 2003 - 06:26 pm:
Thanks Mark. Our GC is now being checked by the supplier and apparently there are problems with the injector.
Regards,
Jan