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dear all,
Variation in study drug concentration, because of different method is
possible?
* 1st time analysis, ESI probe in LC-MS-MS, Methanol was used
as crash solvent and mobile phase was methanol and 0.1% formic acid
This study was repeated ( Repeat analysis) with same conditions
study drug concentration was same compare to 1st analysis
* 2nd time analysis with slight change in mass, extraction and
LC conditions was done this time with APCI ,acetonitrile was used as
a crash solvent and mobile phase is acetonitrile and 0.1% formic acid ,
study drug concentration with 7 fold increase was observed.
Note: this study was performed using different drug stock i.e., this
time stock was weighed again. (We do not doubt the stock as weighing
at both the times were perfect)
Thank & Regards,
M.senthil kumar,
BAR - PCO
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The following message was posted to: PharmPK
Of course it is!!!! Did you validate or characterize the new vs old
method? Apparent recovery and mass might change because of the
possibility
of forming acetonitrile adducts. APCI is gentler than ESI such that
you may
have greater decomposition of your compound with ESI. Your RT, peak
shape
and resolution should have shifted! What provoked the change? Did you
optimize for both? Did you run your old QCs with the new method? You
probably have changed the concentration response relationship and from
that
the LLOQ and ULOQ. A good internal standard (stable label) could
rule out
certain changes but... a systematic cross validation should indicate the
specific changes.
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Dear Senthil, Can you explain, why you have gone for 2nd time analysis
with different method?
L.V.Chakradhar,
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The following message was posted to: PharmPK
Dear Senthil
Its obvious when you change the method the recovery of the drug will
change.
And here you change MS source and extraction method so this can be
happened.
And one thing i am not understanding that why you reanalysis the
subject samples with different conditions.
May this help you
regards
laxman kaswan
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So what exactly was your question?.... why was there an increase in
the signal?
--
Sanjeev Thohan, PhD
SARx Consulting
SARxconsult.at.Gmail.com
http://www.linkedin.com/in/sanjeevthohan
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