ion supression

[Ericz]

To my knowledge, ion supression basically come from two cations (such as Na+) and anions (such as PO4-). The former are competing with H+ in positive mode, and the later one is bonding to the target ion. Both cases result in lower concentration of MH+ in gasous phase.

Could anybody please give more details about ion supression?

Thanks!

[Kostas Petritis]

Ericz,

Normally, in LC-MS, none of the ions that you mentioned should be present in your mobile phase (although there are always Na+ ions that can cluster with your molecules) as they are not volatile.

Now anything that is co-eluting with your compound of interest can cause ion-suppression especially if it has a higher proton affinity (ion positive mode) than you compounds. It has been found that high amounts of non volatile compounds can cause ion suppression independantly their hgih or low proton affinity. Ion-pairing reagents can also cause ion-suppression.

There are several publications that discuss this phenomena...

[MG]

I can't add much to what Kostas said, except to say that some coeluting compounds can cause ion enhancement instead. You may encounter this phenonmenon when attempting to quantitate a target in a biological matrix.