By Anonymous on Wednesday, June 6, 2001 - 06:13 am:
I am working on a quantitative method using the LC-MS 1100. My analyte is 3-methyl,2-aminopyridine. This compound has very poor ionization in the mass spec. Does anyone have any suggestions for a column, buffer or solvent system that may improve the ionization of this compound? I currently use a 10-90% H20+10mM NH4CO2H(pH 3.8)/Acetonitrile gradient, with a
Zorbax XDB C-18, 4.6 X 250mm column, and have very good DAD retention, however the peak for the analyte in the mass spec is in the baseline and
my s/n is very poor. Any comments or suggestions would be greatly appreciated.
By Anonymous on Wednesday, June 6, 2001 - 03:13 pm:
use a shorter column. I don't believe your pH on NH4COOH, use formic acid instead
By Anonymous on Friday, June 8, 2001 - 04:10 am:
I'm sorry let me clarify, the solvent buffered with NH4COOH is adjusted to pH 3.8 with formic acid. This adjustment was made so that my very polar analyte would have better retention in the column. I have also tryed to use a 2.1 X 50mm, 3,5um C-8 column with no improved mass spec results. I orginially ran this analyte with a H20-Acetonitrile+0.1% formic acid gradient, and the RT was >.30mins, eluting at solvent front.
By Anonymous on Friday, June 8, 2001 - 02:51 pm:
This is strange. You are changing the column volume by a factor of 20 and you are not getting any change in s/n? What are the flow rates, and what is your MS detector? Are you splitting?
By Andreas on Sunday, June 10, 2001 - 03:15 am:
Use higher pH>pKa pyridine to have monocation.
By Anonymous on Tuesday, June 12, 2001 - 02:28 pm:
I have and LC/MS 1100, and here are a few
things that I have tried to improve sensitivity.
First, what source are you using? Try
APCI(+); I would be surprised if these
compounds work by any other ionization.
Second, try decreasing your fragmentor
voltage; the molecules may be completely
fragmented at the voltage you are using.
Second, if you have a lot of water in the mobile
phase at the time the analyte elutes, you may
have too much surface tension to ionize the
molecule. Increase parameters such as
drying gas temperature and flow. If you have a
pure solution, I recommend bypassing the
column and using FIA to optimize the MS
conditions. Be sure to do it under solvent
conditions similar to your mobile phase. Also,
be careful about continuously running the
instrument at the upper ends of the MS
conditions, as this can cause wear on the MS.
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