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Dear Colleagues,
We are developing a method for quantitative analysis of mesalamine
which is basic polar in nature and is a zwitter ion with an amino and
carboxyl group. We are trying to develop method for this molecule on
waters Quattro premier but we are getting interference in the blank
plasma sample at the same transition of the molecule. The interference
is more than 20% of LLOQ with a LLOQ of 10 ng. We are getting a
good recovery with SPE on MCX cartridge but we are not able to remove
the interference from the blank plasma. We tried to infuse the blank
plasma sample and found the same transition as of the molecule in the
blank plasma at a higher concentration.
I tried lot of columns including HILIC, Atlantis of waters but I could
not separate the interference.
The Q1 and Q3 mass for the mesalamine is 153.7- 135.9
Can any one help me out in suggesting something which would help me in
removing the interference.
Many thanks in advance.
Parag
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In this case try, change to negative mode or switch to APCI method.
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Dear parag,
Have you tried other transitions? Loss of carboxy in negative mode may
be a good alternative.
At such low masses, solvent clusters from mobile phases may give false
signals. Please make sure blank MP is not having response for the
transition you are using.
Good luck,
Vinayak
Vinayak Nadiger
Manager , Bioanalytical Chemistry
11 Biopolis Way, Helios #08-05
Singapore 138667
E Mail: vnadiger.aaa.combinatorx.com
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Dear Parag
If i were in your place the first thing i would do is to try for
another transition pair, i mean a different Q3 if possible.
I do not know whether you have tried any simple liquid-liquid
extraction procedures
You could try liquid-Liquid extraction procedures after altering the
pH of the biomatrix also, either acidic/ basic pH.
Have you tried anionic catridge also from waters (since ur compund is
a switter ion)
Excuse me if you have done all these. These are some thoughts.
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Can you try derivatizing. FMOC or ethyl chloroformate can overcome
this. The derivatization involves just 5 min time.
Regds
Rajan S. Kombu
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If you're speaking of 5 amino-salicylic acid, then try an MTBE based
extraction under acidic and/or basic conditions, as well as using
ACN:MeOH as a 1:1 for an organic mobile phase. Have you tried some fo
teh MACMOD columns? The suggestions of using different transitions is
a great idea, but you'll have to hit this one pretty hard under ESI to
get fragments under 100 AMU. It should be feasible.
Sanjeev Thohan
Director DMPK
Exelixis, Inc
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