Increase sensitivity on MS/MS

[carolina.nebot]

Hi all,

I am working with a HPLC-MS/MS and I would like to increase the sensitivity in the method to be able to detec lower concentration. Do you know which parameters I have to change to increse sensitivity on the method? I am doing MRM chromatogram but my lower concentration is 100ug/l and I would like to go to 1ug/l more o less.

Thank you

[Kostas Petritis]

Carolina,

Things are not as easy and improvements can come from different places. MS sensitivity depends on many things and the composition of your mobile phase is one of them (i.e. you can expect of having good sensitivity with an aqueous mobile phase). The use of the right mobile phase additives can also improve your sensitivity.

I am not going to get on to details on this part...

About the MS, there are two things you should do. One is to apply the right voltages on your electrospray tip as well as your orifice and cone voltages in order to have the highest abundance possible of parent ion getting in the MS and then you want to pick up the right collision energy (eV) in order which will give the most intense product ion (and that is the one you should choose).

Everything is a question of compromise. The gas adjastement will better dessolvate your ion of interest but too much gas and you will have in source fragmentation. Same with orrifice and cone voltages you want to optimize them to have the highest possible intensity of your parent ion. Same with the CAD voltages you want to use the right collision energy that favorise the most intense product ion.

Some of the above are discussed in Petritis et al., Parameter optimization for the analysis of underivatized protein amino acids by liquid chromatography and ionspray tandem mass spectrometry. J. Chromatogr. A 896 (2000) 253-263.

Good luck,

Kostas

[Uwe Neue]

Many people are using MS to get a specific detection of the analyte(s) in a background of matrix. If this is your analytical problem, you can get much improvement in sensitivity by removing the background with appropriate sample preparation techniques. If this is the problem, I can give you much more advice after you describe a few more details.

[carolina.nebot]

Hi,
Thanks for yours help,
My mobile phase is methanol, water and 10mM of ammonium acetate 10% (isocratic for the NH4Ac). Any suggestion will be good

Thanks again, :