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We have developed a method for quantitative analysis of oxcarbazepine
and its metabolite hydroxycarbazepine in human plasma using
carbamazepine as internal standard by LC - MS - MS (MRM scan typne).
It is a well known fact that MRM is specific. But in carbamazepine
chromatogram (internal standard) we observed one well separated peak
which is similar to the retention time of hydroxycarbazepine
(metabolite). The intensity of this peak is increasing with the
increase in concentration of analyte. The retention times of
oxcarbazepine, hydroxycarbazepine and carbamazepine are 1.51 min,
1.84 min and 2.45 min respectiviely.
The Q1 and Q3 masses are as follows
oxcarbazepine 253.0 - 236.0
Hydroxycarbazepine 255.1 - 237.0
Carbamazepine 237.0 - 194.1
It is very helpful to me if anyone can solve this problem
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The following message was posted to: PharmPK
Hydroxycarbazepine may be having a cross talk in carbamazapine
channel. You may wish to change the MRM transition used and see
whether it works. If not, How about using another analog of same
class of comppounds as an internal standard?
On a separate note, can I have opinion of others on specificity of
MRM mode? I think mass spec vendors have oversold the concept of
specificity of MRM detection. I have seen unexplained peaks in MRM
chromatograms, probably contributed by endogenous components.
My experience is, there are cases where cross talk contributes to the
extent of 10 %.
Manager , Bioanalytical Chemistry
11 Biopolis Way, Helios #08-05
Office 65-6773 7908
E Mail: vnadiger.-at-.combinatorx.com
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