I am currently working on a CE-MS system, MS being Agilent 6230. I use the system in the positive mode and the capillary voltage is set at 5500 V. And the system works properly.
I'm a bit curious about the effect this might have on the detector, since the recommended range is up to 6000 V, and 5500 V seems rather high.
Does anyone have experience with this kind of setting? Is there some long-term adverse effect that I need to worry about?
Hi Wei,
The capillary voltage affects the integrity of the capillary you're using to electrospray a protein-containing solution. Over time, the capillary (coating) will diminsh, which you can temporarily counteract by increasing the voltage up and until the point that that no longer helps either.
At that point, replacing the capillary is your only option.
I'm not sure how you see this influencing your detector?
In some cases, mass detectors contain electron multiplier tubes that generate the actual output signal once an ion is detected. These also require a certain voltage to function properly, which should be increased over time due, mainly due to the same reasons as for your capillary. Eventually, these multiplier tubes also have to be replaced.
Hope this helps.
Hello, Wei,
a high capillary voltage can lead to reductive or oxidative processes that are not desired. It can also lead to an undesired reduction in signal intensity due to discharge effects. There is not one capillary voltage that is optimal for all your compounds. It must often be optimized for each compound (especially if you want to quantify). Also feeding of additives (e.g. isopropanol/propanoic acid in a ratio of 1:3) can reduce negative suppression effects (e.g. by TFA). Full throttle with the ESI parameters often does not lead to the optimum. Less is often more.
Regards Markus
P.S.: The links give a short introduction to the topic of electrospray and its optimization.
http://www.chromatographyonline.com/secrets-electrospray-ionization-why-less-more-0
Article Selection of the Optimum Electrospray Voltage for Gradient E...
http://www.ecu.edu/cs-cas/chem/upload/EnkeESI.pdf
http://quimica.udea.edu.co/~carlopez/cromatohplc/effect-eluent-ionization-process-lc-ms-2009.pdf
http://www.eurekaselect.com/134832/article
An ce-ms interface consists out of 3 stages: ce part, ionization part (esi), ms part (atmosphere/vacuum, mass filter, ion detector). All of them with there own high tension -and for you more important : current) settings. Somewhere between the CE part and the vacuum interphase there is a ground( zero potential) level. Depending on the location of this point (I don't know your device) there might be interaction between the ce and the esi, changing the current in the ce capillary ( Kirchhoff's circuit law ) in witch case you have to do some calculations. For example the (old) sciex API III has the vacuum interphase grounded so part of the esi current will be drawn from the capillary; the bruker esquire 3000 has the esi needle grounded so no problem at all.
However for your question of effects between the ce and the detector, they are electrically so far away from each other that there is no direct influence between the both. This thus not mean that the ce high tension has no influence on the detected amount, see previous comments
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