Chromatography Forum

Hi all,

We use a SPE elution solution with an percentage of 32% ammonia solution.
We know this to be a critical step for the ellution process.

On the last months we have been slowly loosing S/N in our lc-MS/MS results and we suspect the ammonia solution could be losing strength.

We would like to verify if the solution is still good enough.
pH verification wasnt a big help since Merk datasheet only specifies that pH is "strongly basic".
Any way we mesured a pH of 14.05

Does anyone knows how to check if a solution like this is still close to what it was when we first open it?

PS. Compare with an extration done with a new Ammonia botle would solve it, but buying anything around here is always a complicated process, specially when we arent even sure that it is the problem.

Thanks everyone for you time and good luck with your challenges!

Titration. For acid/base titration, you will have to use a back titration. There are a number of examples of back titration on the web.

There are other techniques, but you would most likely have start with some purchases. And even the titration requires a burette and a known standard to start with.

Added in edit: There are physical properties that could be helpful, but would requie apparatus for measurement (http://www.tannerind.com/PDF/green-aqua-amm.pdf) - and you may have the capabilty to measure specific gravity close by...

And, having given this, you can have loss of ammonia from evaporation - or nutralization (and salt formation) by adsorbtion of some acidic compound from the laboratory air. You may or may not get an indication of adsorbtion of the acidic compund by the physical property mesurements.

You are right, we would need a standard acid wich we do not have, but thanks for the sugestion.

I guess we will try to increase the amount of the 32% ammonia solution in the mixture and see if there is an increase to the original S/N ratio we used to see.

Thank you all for your time.

Titration it is (we have made and assayed household ammonia products). Back titration isn't really necessary, can titrate with acid to the methyl red end point.


If you don't have standard acid, you could standardize what you have v. sodium carbonate from a swimming pool store.

Reading back throgh the post... The elution process and the ionization process are not the same thing. If the ammonia is part of the buffer and the peak is eluting at the right time, the buffer might be right.

What maintanance have you been doing on the LC-MS/MS? Any source cleaning, cleaning of the nebulizer, cleaning of first Quadropole stage(s)?

Hi,

First of all, thank you all for your interest and help!

We have tried incresing the percentage of amonia in the SPE ellution mixture with no better results.

We have tried a new column, cone cleaning, calibration, manual mass re-evaluation of the compounds.
Nothing of this have got any better results.

We have tried new solutions that we know the extration is sensitive about.
But also with out any changes.

We see sensitivity go up and down, and on the long run its getting more down than up.
We haven´t done any kind of cleaning inside the MS/MS.

And we are starting to believe that this has something to do with the high number of samples we have been injecting.
Maybe it depends on what someone else have been injecting before we did, or how long was the equipment with out injecting anything until we do another set.

We dont know.
Next step will be to show our control chart to some expert from Waters.

Thank you all.
If you have anymore ideas, we will be very glad to hear them!

Hi,
We see sensitivity go up and down, and on the long run its getting more down than up.
We haven´t done any kind of cleaning inside the MS/MS.

We have a Thermo MSQ here in the lab with similar behaviour. As these machines don't have sheath or curtain or whatever it is called by the different vendors gas that keeps dirt away from the inside, cleaning the cone is not sufficient. Therefore I also clean the RF lens rather frequently (depending on sample load and matrix, up to twice per week). This is annoying but the only chance for me to keep sensitivity up.

Joerg

Ammonia water is cheap, so I would just remake the solutions periodically or set up a robust and quick titration system to check strength. You maight want to consider cleanign the quadrupole itself as well. We do that from time to time on our quadrupole - Orbitrap hybrid MS.