I was calibrating our LTQ-Orbitrap XL and I noticed very unstable ESI spray (~40% RSD in the API stability evaluation). I changed the spray voltage, sheath and Aux gas flow and the position of spray needle, but nothing worked. Could anybody tell me what I should do next?
Check the spray tip and assembly with a magnifier for irregularities. Small deformations , deposits or misalignment here have a huge effect.
What sample were you spraying; did it have some organic solvent such as acetonitrile or methanol or ethanol? Addition of some organic solvent can improve the spray. Else, there can be some block in the spray capillary/needle. Either change to a new spray capillary/needle or clean the spray capillary/needle. What was the spray voltage? Altering the spray voltage also can help in obtaining a good spray. Hope these suggestions are useful to shoot the trouble. Let me know, what happens. Sabareesh.
which flow of HPLC or syringe are you using ? Using a lower flow rate maybe can help.
When you already checked the gas flows and the position of the spray needle, I would suggest to
1. Did you check the connection between syringe with calibration mixture and the inlet of ESI source? Maybe it is leaking.
2. Did you change Transfertube to check whether it is blocked? A change in intensity of iones could be a indication.
3. Change the needle to see whether the needle is blocked?
4. It is also possible that some ion optic parameters are changed. So you can also check this.
As Hector Koolen mentions, flow rate is important. Setting appropriate flow rate can help in getting good spray. Sabareesh.
Thank you very much everybody for answering my question. I appreciate all.
Based on everybody's comments, I think I should try to change or clean syringe needle, spray needle and transfertube. The flow rate of syringe pump is 5 uL/min and already checked spray voltage by changing it. I also did tuning, so ion optic parameters could be OK.
Hello everyone. I changed the spray needle to new one, and that solved the problem! Now the ~ 5% RSD in the API stability evaluation. Awesome!. Thank you all answering my question.
Good to know that good spray was obtained with a new spray needle. I think, flow rate of 10 or 15 or up to about 20 microlt./min. can be better than 5 microlt./min., although it is known that the lower flow rate can give better quality data. Sabareesh.
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