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Dear All,
We have a Agilent GCMS (6890 GC with 5975 Mass selective detector) which is giving inconsistent/irreproducible peak areas when injected repeatedly with a specific concentration of methyl stearate dissolved in dichloro methane. What could be the reason for this inconsistency. Kindly help me with this issue.
Thank You,
Krishna
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Good trouble shooting dependes on the information provided- and you haven't given any. 1) Is this a validated system that is did ithe chromatograph and the MS pass IQ/OQ/PQ?
2) Are the injections reference material in volatile solvent or are they extracts?
You need to determine if the issue is with your analytical instrumentation or with your extraction process.
It could also be with the compound itself.
-- Edward F. O'Connor
78 Marbern Drive
Suffield, Ct 06078-1533
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The following message was posted to: PharmPK
Dear Krishna,
I used to analyse samples on GC long ago. One immediate thing comes to
my mind is aged septa. Please use new Septa and check.
Regards,
Vinayak
Vinayak Nadiger
Manager, Bioanalytical
Forma Therapeutics(Singapore)
11,Biopolis Way ,Helios # 08-05
Singapore 1386607
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Dear Ed,
Thank you for the reply. The GCMS is validated. Methyl stearate is a reference material dissolved in toluene. We inject methyl stearate everyday to see whether the peak area and peak height are of desired intensity and this tells us that everything is fine with the GCMS. Methyl stearate in not from any extracetd samples. It is just spiked methyl stearate standard in toluene. I am guessing the problem might be due to the instrument.
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Disconnect then reconnect the column. You may want to sacrifice 2-10 mm at each end. Put a new insert in-with liner of glass wool. Check chromatography and reproducibility. Can you run FID and not MS to isolate detector?
-- Edward F. O'Connor
78 Marbern Drive
Suffield, Ct 06078-1533
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