Lost sensitivity on our LC-MS/MS

[Tommy Krak]

Greetings All,

Sensitivity has been lost on a Quattro Premier XE for the positive ion mode in ESI and no longer meets the specified S/N ratio for reserpine (609 to 195 transition) of 500.

The S/N ratio which has been determined is about 140.

So far I have cleaned the ion block (including all parts contained in the ion-block) and rebuilt the probe (i.e. replace the capillary).

Any suggestions and/or thoughts on this topic would be much appreciated.

Cheers,

Tom

[orcicdejan]

Well, first, I would check whether S/N is decreased due to signal decrease, or noise increase!

[2606cind]

maybe,first you can do the autotune,check the sensitivty of the instrument, and then check the noise .

[sam.pedraglio]

Have you lost your sensitivity with every compound or only with Reserpine?
How is the sensitivity in Negative?
Have you tried to clean the T-Wave?

[Tommy Krak]

The sensitivity has only been lost for reserpine. I have not tried -ve ion ESI. I have cleaned the T-Wave, though admitedly not lately. I shall try cleaning the T-Wave.

Cheers,

Tom

[sam.pedraglio]

The sensitivity has only been lost for reserpine.

In this case I'd try a new fresh bottle of Reserpine.

[Kostas Petritis]

I hope Tom means that he only tried reserpine...

[sam.pedraglio]

I hope so, but never say never.

[gxch43]

I hope so too, and can you post the old and new diagrams of reserpine?

have you tried other compounds?

[Tommy Krak]

So the situation is resolved and I would like to tell those who are interested how it was resolved.

We are now getting S/N ratios exceeding the spec for reserpine for the 609 to 195 transition.

The error occurred as a result of putting the probe together incorrectly, not that the parts were put in wrong. If you are familiar with the Waters Quattro Premier XE. When the ESI Probe was re-assembled, a piece of PEEK tubing was used on one side of the PEEK union (which was used to bottom-out the ESI Capillary, I imagine the capillary could have gone through the centre hole as well). However, the PTFE "Tube Liner" was not bottomed-out on the tube stop of the PEEK Union, this created a dead volume.

When re-assembling the probe ensure that the PTFE Tube Liner is bottomed-out in the PEEK Union. In our lab we have noticed that these liners are not cut squarely, it was suggested that we trim off as little as possible from the PTFE Tube Liner to ensure that it is squarely cut before installing it, this will reduce the dead volume.

Thank you all very much for your responses. If anyone else expriences this problem, I hope I have been able to help!

Cheers,

Tom