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Dear group members,
Welcoming the LC-MS/MS users to comment on the plausible causes for
high background noise observed sometimes in LC-MS/MS analysis. What
are the different attributing factors responsible for high to very
high baseline level and what are the different measures to reduce the
baseline.
Also how best can we explain the rise in baseline level while doing
analysis in SIM mode compared to MRM mode.
Looking forward to have your responses.
Regards
Neel K Mohan
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The following message was posted to: PharmPK
Hi,
If your molercule has a low FW, then the baseline can
be high. If possible you could try negative mode which
usually can give a lower baseline. Could you also
check your column, I mean changing to a new column
with the same type. In addition, if there is something
wrong in the gas flow pass in your ms which could also
causes high baseline.
These are just some thoughts.
Xiaodong Shen
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Hi, Neel !
A rise in a baseline noise is frequently observed when a large number
of samples with high injection volume and heavy matrix contamination
are analyzed.
There are number steps you can take to avoid this problem:
1. Clean your LC-MS interface (ESI, APCI) more often.
2. Use a flow diverter valve in front of a MS to prevent matrix peaks
to enter the MS.
3. Use a flow splitter. Usually, only a 1/10th or 1/5th of a HPLC
flow is neccessary for a good signal/noise ratio on MS/MS.
4. Let a low flow rate of 50 % MeOH or 50 % Acetonitrile to be
infused into MS after analyses and between analyses.
5. Use MRM or SRM mode for data aquisition.
6. Improve your sample cleanup to reduce heavy matrix loading. Reduce
injection volume.
7. Improve your chromatographic method to separate your analytes from
matrix peaks.
8. Use only LC-MS gradient solvents and LC-MS compatible columns with
low stationary phase bleeding.
Best regards,
Jurij Trontelj
Faculty of Pharmacy
University in Ljubljana
Slovenia
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The following message was posted to: PharmPK
Dear Neel,
Baseline noise can be caused by both LC as well as MS parameters,
High noise due to high buffer capacity for example 2mM buffer will give
a better baseline than for 10 or 20mM buffer for some molecule.
Mobile phase composition with high aqueous percentage also may cause
problem with noise, also the flow rate of mobile phase sometimes may be
the cause for the same.
Flow rate is also a parameter for proper nebulization in MS and source
parameters with high gas settings may also cause problem. Improper spray
and positioning of MS capillary needle sometimes brings high noise for
some molecules.
Last but not the least rinsing solution modification also helps
sometimes to resolve baseline noise issues for some molecules.
Hope this works , any further query is always welcome,
Regards,
Dipanjan
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The following message was posted to: PharmPK
Hi Depanjan,
I do agree only some extent, what you had posted on 8th jun 07. But, can
you explain one thing, during quantification in MRM mode for most of
molecule, noise background always less than compare to SIM
quantification in same chromatographic condition and sample preparation.
Regards
Ajit Kumar Singh
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Dear Mr. Ajit,
I appreciate your interest and keen observation and here is the
simple interpretation.In SIM mode single quad is involved that is Q1
only.The background noise of entire region contributed by solvent,
mobile phase,for example a mass of 256 scanned sometimes show a
background noise of 1e-4. But in MRM involvement of Q1 and Q3 only
for example for mass of 256 fragment 156 will only be captured. Other
mass will be filtered background noise will be very less as only the
fragment of Q1 will be selected and detected as compared to SIM.
hope this works
Regards,
Dipanjan Goswami
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