Ion Suppression is one of the biggest problems in ESI. If your sample contains any of the species listed below, then it is possible that while your analyte is present in your sample, it may not be observed! Not only this but contaminating the system with materials like TFA, TEA etc may cause similar issues for other users. PLEASE AVOID USING THESE ADDITIVES IF AT ALL POSSIBLE OR SPEAK WITH US BEFORE RUNNING YOUR SAMPLES.
-
Suppression:
- Competition and interference with analyte ionization resulting in decreased number of [M+H]+ or [M-H]- ions
- Will result in decreased sensitivity and in the worst case scenario, the analyte may not be seen!!
- Especially prevalent with ESI, less so for other API methods and MALDI
- Sample preparation and clean-up are VERY important to minimize this problem
- Sometimes the chromatographic process can be a very effective cure but is not a magic wand and must be evaluated carefully
- In qualitative analysis ie non-targeted, this problem can be very difficult to measure
- In quantitative analysis ie targeted, isotopically labelled internal standards can compensate for ion suppression effects ie 13C or 2H
-
Caused
by
salts
that
form
adducts/clusters
with
analyte
and/or
sample
contaminants:
- Strong bases in positive mode eg triethylamine (TEA)
- Acids in negative mode eg trifluoracetic acid (TFA)
- Non-volatile buffers (phosphate, TRIS, HEPES, SDS etc), detergents, other low molecular weight cationic and anionic species (Na+, Cl- etc) and ion-pair reagents
- Non-covalent dimers [2M+H]+, trimers....
- Metal ion complexes, e.g. [2M+Cu]+, Cu+ eg from LC equipment
- Other contaminants in the system eg PEG, PPG, platicizers, residual matrix species, non-volatile buffers.........
- Co-eluting analytes with different proton affinities that is, analytes that compete for protons - problematic for qualitative analysis of complex mixtures