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Dear chromatographers,
Can any one suggest how to increase the sensitivity in LC-MS-MS for
acidic, basic and neutral molecules.
a) Is there any relation established between lowering the ion source
temperature and sensitivity of the analyte (as it is source parameter)
b) Is the earlier statement hold good only for adduct formation of
analyte.
Thank you for your answers in advence
Regards
Subramanian
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The following message was posted to: PharmPK
Dear Colleagues,
Concerning temperature and ion source, in electrospray (ESI) the
temperature influences desolvation: higher temperatures allow better
desolvation, particularly important when using high flows and high
water content. The position of probe compared to orifice will also
play, depending on desolvation and distance the ions are sampled in
different parts of the plume.
We experienced significant differences in response (and linearity)
depending on temperature, gas flows and position of probe; some
instruments (eg. Waters) might be more prone than others to such
effects.
In APCI sufficient temperature is necessary for full vaporisation.
Temperature might degrade thermo labile molecules but in general such
products are entirely lost in APCI, whilst they are generally stable
in ESI.
Patrice Larger
Bioanalytical Sciences
The R&D Division of Rottapharm SpA
E-mail: patrice.larger.-a-.rottapharm.com
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The following message was posted to: PharmPK
Subramanian,
Ion source temperature is a very important parameter with respect to
sensitivity. But it is instrument and compound dependent. (Which MS
platform are you using?) Your objective is complete desolvation
without heat degredation. While running at high source temp, however,
you should remember that desolvation/evaporation provides a
significant protective cooling effect. As the flow becomes higher,
and water content higher, temperature and gas flow should generally
increase to compensate.
It is important to optimize your compound finally under actual HPLC
flow conditions - ideally at the flow and % organic where your analyte
is eluting. (% organic also has a major influence on desolvation.
High organic sprays better in general.)
Good luck,
--
Stuart Coleman, Manager
Matrix BioAnalytical Laboratories
25 Science Park at Yale
New Haven, CT 06511
Web: www.matrixbioanalytical.com
Email: stuart.coleman.-at-.matrixbioanalytical.com
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Thank you for your suggestion on ion source temperature. I was facing
a problem in MS analysis that the response of my compoundwa increasing
after some number of injections.What are the reasons for sudden
increasing/decreasing of response in MS analysis.
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The following message was posted to: PharmPK
Dear suresh,
a) It may be problem with your autosampler. Donot try to inject samples
immediately after sample processing when you are maintaining autosampler
temperature. Try to preexpose to that temperature.
b)Is the instrument stabilized for a specified amount of time.
c) When the curtain plate is removed for cleanup, you should not
straight away submit the samples after replacement. Try to stabilize the
instrument for atleast 1hour.
D)It may be due to carryover. Try to inject a blank after injecting ULQ.
By this you can conclude whether carryover is there or not.
E) Are you using IS for your method?
F)Is response more for both IS and Analyte?
With Regards,
Veeravalli Vijaya Bhaskar,
Research Associate,
Aurigene Discovery Technologies Limited,
Bioanalytical Division,
Bangalore,
Email: vijayb.aaa.aurigene.com
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Hi Bhaskar,
Thanks for your explanation, yes iam using IS for my
method and the response proble is with IS not for the Analyte. Maybe
the temperature will effecting the analysis. I will workout with your
suggestion.
thank you
Regards
Suresh Dama
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Hello Suresh,
When the analyte and IS are structually similar then they will respond
in a similar way to the changes the mass spec conditions during the
run. If you are using a structurally dissimilar compound as your IS
then may be this should solve the above mentioned problem.
Good Luck
Ravi
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