Chromatography Forum

Hi, there,

I am seeing gradual response drop when injecting same extracted sample (protein precipitation) for ESI+ analysis. After the system was idle for some time, the response came back but dropped again with injections. Is this mainly due to matrix effect on my column or matrix effect on the ionization process or something else? How to solve the problem? Any suggestion is appreciated.

Regards

Linda

Linda,

Yes, these are matrix effects of very polar compounds eluted at the beginning of your chromatogram. These can be salts and other polar compounds that create a drop in your TIC. The quantification of any compounds of interest eluted at that point would be problematic so you must be sure that these are eluted in an area that you do not have ion-suppression from the matrix.

There are some ways to decrease matrix effects... in general a better/different extraction and/or if your MS sensitivity allows dilution of your injected sample etc. However, you always have some matrix effect close to the void volume...

Kostas

Be sure that your chromatography is ok, so create enough retention for the components you want to analyse. The compounds, eluting at the beginning of your analytical run can also faul the source of your MS. You can use a switching valve to prevent this part of the run to enter your MS

regards Bert

I agree with Bert.
Some compounds have negative influence on ionisation for some time after their eluation. Those compounds show some kind of vereberation inside the ionisation chamber. In such cases it is very important to cut them away (means switch them to waste).

The ion suppression can also be caused by nonpolar compounds that pile-up on your column and elute in later gradients. If this is the problem, a column wash with a strong solvent at the end of each gradient will help. I also recommend using a divert valve. Divert the eluent to waste at the beginning (void volume) and end (column wash) of your run.