Chromatography Forum

Hello,
I am new in this forum and I really hope that you can help me.
We have an Ion trap 500MS with ESI from Varian. One month ago we changed one of the turbo pumps. After restarting the machine the sensitivity was very bad and the needle glew blue. We did not change any of the parameters of the ESI, also the voltage of the needle ist the same (4-5kV). We also changed the needle. Do you have an idea what happened? We still have big problems with the sensitivity.

is there any liquid making it into the spray chamber?
Have you got the spray needle in exactly the same place as it always was?

We did not change the needle position. The chamber is closed besides there the solvents running through the needle. What do you mean exactly?

Is it arcing?

Yes it is arcing. You can see a blue glowing tip of the needle with the same voltage than before.
When we swith of the ESI we can see the droplets coming out of the needle. It is not blocked.

It's a typical outcome when the capillary voltage is too high. Look like you may have a faulty voltage control. Call and talk to your service engineer

sorry not to have replied earlier. Yes, I was asking whether droplets were coming out of the needle, as on some systems, in the absence of any solvent flow (i.e. when the needle is blocked or the hplc isn't working properly for some reason) a glow appears.

Also I asked about needle position, because the glow depends on the strength of the electric field, so if you put a needle at the same voltage, closer to grounded parts of the spray chamber, it will start to glow.

It sounds like you've done all the right things, so if the liquid supply is normal, and the voltage claims to be right, maybe it isn't right and the electronics are wrong.

However, I'm assuming you haven't got a very salty buffer for some reason?

The glowing of our needle stopped. I cannot really say why because I did not change the needle position. Then I bought a new needle.

But the sensitivity is still low. We have the following problems.

1. no tuning: trap frecuency failed

2. The higher masses of the tuning solution (1000-2000) are very very low in positive mode. High background at lower masses. In negative mode ok.

3. Signal decreases within direct injection at stable flow rate.

No, we do not have a salty buffer. We run our system with MeOH/ Water with low amounts of acetic acid.

We also think it could be an electronic problem. Or not?

molekat,

Just curious, is there a nitrogen purge gas or bath gas in this system or not?

Best regards.

We use nitrogen as nebulizing gas (+ESI) and drying gas and helium as CID gas.