Back to the Top
I also agree with all the responders.
Pl check the instrument response in direct infusion mode with PPG (a calibration standard). Check the response stability (906 m/z) in Q1 and Q3 for at least 30 min. If you observe downward trend, then ask instrument engineer to clean the respective Q and additionally Qo. I would also recommend to change the solvent grade and water source.
regards,
Jignesh
Back to the Top
The following message was posted to: PharmPK
Happy new year to group. Sorry for late response, but thought of
sharing our recent experience.
This kinf of situation is peculiar and will easily lead trouble
shooting in a wrong direction. I would like to share our recent problem
with 3200 Qtrap.
We saw decreasing response for analyte in MRM mode. After ruling out all
chromatography related issues, mass spec was suspected. To our surprise,
PPG showed expected response at m/z 906. When I insisted, there is
problem with mass spec, engineers checked PPG response at other masses,
and realized that there is charging in low mass range, and thus
affecting small molecule response!!!!
Then whole mass rail was cleaned. After brief run, to our surprise,
charging returned again, this time it was only on Q0. After cleaning
Q0,now mass spec response is stable for more than 3 months. Hope this is
some useful info to the group.
Regards,
Vinayak Nadiger
Vinayak Nadiger
Manager, Bioanalytical
Forma Therapeutics(Singapore)
11,Biopolis Way ,Helios # 08-05
Singapore 1386607
Back to the Top
Hi Ning,
The compound seems to be stable (based on it UV profile).If the decrease in response is seen during ESI tuning over a period of time, I feel the problem resides with the ESI probe..please check for charring/blackening of the probe/capillary due to which the voltage is not uniform on the probe..hope it helps!
-AB Rao
Back to the Top
The following message was posted to: PharmPK
1) is the IS a stable label? Is the analyte response the same in the
presence and absence of IS?
2) Have you tried running a double gradient-1 injection but two cycles
of gradient?
3) What Frits are you using-titanium, SS, Peek
Back to the Top
Hi Ning,
I agree all the comments.
I have the same problem. However, It is my IS signal decrease with time last.
in the high analyte concentration samples, the signal of my IS dropped half.
maybe there are some competation btween your sample and IS while ionization.
try to use another IS or change MB to separate your analyte and IS. hope it helps,
Chang
Email:chg-wang.aaa.hotmail.com
Back to the Top
Many thanks for every reply. There are something can be comfirmed: 1, The compound is stable.
2, No problem with ESI probe, since we had changed and compared the response.
3, IS seemed not interfer the ioniation of the compound(we had compared with different IS).
4, We use PEEK, and I don't think it the compund will absorpted onto the PEEK (we changed new PEEK piples)
5, two gradients cycles in one injection had been tried, it's the same.
6, The compound was firstly disovled in DMSO, then futher dilvent with ACN. (we also tried the solvent without DMSO, only ACN)
We're cleaning the Q0 ourselves, if the problem is still there, we will ask the engineer to clean the Q1/3. God bless me.
Thanks again and Happy New Year, I'll let you know the results
Ning Lei
Back to the Top
Following information, we cleaned Q0, not work. Adviced as the service engineering, using PPG, we shift between the positive and negative ESI model did not effect the response of PPG, that means the Q1 and Q3 are not charging. Nightmare still there.
2011-01-10
Ning Lei
Back to the Top
The following message was posted to: PharmPK
Can you change the mass you are monitoring or monitor the parent?
Back to the Top
The following message was posted to: PharmPK
Have you cleaned complete mass rail?
Did you check PPG response at low mass range?
Vinayak
Back to the Top
Yes, We had used different daughter mass, even tried MIM (parent/parent) with low CE.
2011-01-13
Ning Lei
Back to the Top
Till now, I think also the instrumental problem can be excluded. Since there a piperazine in the side chain of this compound(R), and the different pH condition will lead two kind of salts, R.HCl or R.2HCl. I was wondering if the gradient we used changed the pH values of the MP, make these two salts deposite at the column, and thus made the Mass signal unstable. Any suggestion? Still a nightmare.
Ning
|
Want to post a follow-up message on this topic?
If this link does not work with your browser send a follow-up message to PharmPK@boomer.org with "Decreased mass signal" as the subject | Support PharmPK by using the |
Copyright 1995-2011 David W. A. Bourne (david@boomer.org)