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hi all,
we are trying to devolop a LC-MS/MS method for a NCE.
the peaks for NCE&IS were good and there is clear resolution of two
peaks.
but in the system suitability studies, we were unable to get the same
response
(peak height) on repeated injections of the same sample
(ratio between NCE & IS is constant with decreased response also).
there is no problem with instrument as it is a new one and
validated recently.
what might be the problem?
nag.
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Hi, Nag,
Did you use TFA in the mobile phase? We observed similar problem before
and
found it was all TFA's fault.
Jim J. Xiao
Division of Pharmaceutics,
College of Pharmacy,
the Ohio-State University
496 w. 12th Ave, Columbus, OH43210
Phone: 614-6884328
Email: xiao.25.at.osu.edu
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Dear Nag,
I have seen similar results when a gradient is not extended past the
point
where the analyte elutes. Tight binding impurities may migrate only a
fraction of the column length at the top of the gradient before the
percent
organic is decreased and the impurities stop migrating. Because of
this, it
may take several injections before there is interference in the analyte
ionization. If this is the source of your problem, it can be resolved
by
further extending the gradient or cleaning up the sample prior to
injection.
Good luck with your method.
Mike
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Hi,
Sometimes constant decrease in collision gas will result in reduced
response. Please note down pressures of collision gas before and after
run,
see whether it helps.
Vinayak
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Hi Nag. and all,
You can try to divert the mobile phase corresponding to the solvent
front to the waste. The solvent front may dirty the source and
progressively sensitivity decreases. While the mobile phase is
diverted, you should replace by a cleaning solvent (MeOH or ACN/H2O
with or without 0.1% formic acid) delivered by an additionnal LC pump
via a 6-ports valve.
Hope this help
Henri Benech
CEA, France
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