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- Posts: 15
- Joined: Fri Oct 21, 2016 2:01 pm
Hello forum,
we run out of ideas.
We bought a new instrument and face extreme difficulties to achieve stable conditions.
To keep things simple, we use a n-alkane standard (containing nC10 – nC40 in n-hexane, 4ng/µl each).
The symptoms of the last run on this instrument:
• With n=8 consecutive injections it is hard to get near a RSD of 5%.
• Each run shows an increase in abundance. Increase in peak area goes up about 20%-50%(from first to last run) depending on the n-alkane.
• Before and after the sequence (2 blanks, the 8 standards mentioned above, 1 blank) the abundance of the PFTBA fragment 69mz increased from 290k to over 400k, EMV stays at the value derived from the tuning. Air/Water check always turns out okay.
Other varieties are decreasing area counts of the alkane standard and PFTBA fragments. It is very hard to narrow the cause down.
We even went from splitless to split (3:1 and 5:1) and tried different tunes even (e.g. a-Tune to use the extractor source as a SS-source to simplify this even more), but, stable conditions were never achieved.
As Agilent has a checkout method (single SIM for OFN and runtimes of 6 minutes) not adequate for observing these issue it seems, the instrument is OK in their opinion, no further action needed.
The Instruments:
Agilent GC8890 and MSD 5977B
Splitless injection of 1µL
Agilent DB5-30x0.25x0.25
42°C to 325°C with 5.52°C/min and final hold for 10 minutes, total of 61.8 minutes
Transfer line at 280°C
Xtr EI 350 Source
Has anyone experienced a similar unstable/erratic behaviour? What could cause these shifting intensities? We appreciate every hint.
Thank you!
we run out of ideas.
We bought a new instrument and face extreme difficulties to achieve stable conditions.
To keep things simple, we use a n-alkane standard (containing nC10 – nC40 in n-hexane, 4ng/µl each).
The symptoms of the last run on this instrument:
• With n=8 consecutive injections it is hard to get near a RSD of 5%.
• Each run shows an increase in abundance. Increase in peak area goes up about 20%-50%(from first to last run) depending on the n-alkane.
• Before and after the sequence (2 blanks, the 8 standards mentioned above, 1 blank) the abundance of the PFTBA fragment 69mz increased from 290k to over 400k, EMV stays at the value derived from the tuning. Air/Water check always turns out okay.
Other varieties are decreasing area counts of the alkane standard and PFTBA fragments. It is very hard to narrow the cause down.
We even went from splitless to split (3:1 and 5:1) and tried different tunes even (e.g. a-Tune to use the extractor source as a SS-source to simplify this even more), but, stable conditions were never achieved.
As Agilent has a checkout method (single SIM for OFN and runtimes of 6 minutes) not adequate for observing these issue it seems, the instrument is OK in their opinion, no further action needed.
The Instruments:
Agilent GC8890 and MSD 5977B
Splitless injection of 1µL
Agilent DB5-30x0.25x0.25
42°C to 325°C with 5.52°C/min and final hold for 10 minutes, total of 61.8 minutes
Transfer line at 280°C
Xtr EI 350 Source
Has anyone experienced a similar unstable/erratic behaviour? What could cause these shifting intensities? We appreciate every hint.
Thank you!
