Page 1 of 1
How can I improve the sensitivity of sample in LC-MS
Posted: Thu Apr 21, 2005 8:32 pm
by dudi
My sample has strong UV absorbance but no peak in MS in both mode of +ev and -ev in buffer formic acid and ammonium format. The sample is unknown. Did you meet this kind of sample? what kind of compounds can happen. How can I improve it.
I appreciate your reply.
Posted: Fri Apr 22, 2005 1:46 pm
by MG
It is possible for this to happen. An aromatic or unsaturated hydrocarbon could have good UV response but little or no response in ESI, or even APCI. If you have tried only ESI, try switching to APCI if available, and run in both polarities. If that doesn't work, then photoionization is another option. For some less polar compounds, it is also possible to add sodium acetate (~ 5 to 50 micromolar) to the mobile phase to form sodium adducts in ESI positive, where proton adducts will not form.
Posted: Tue Apr 26, 2005 3:36 am
by mass
Some times PH adjustment is also causes the problem for ion supression.
so first you will try with infusion by dissolving your compound in methanol. Then you came to know that which mode it is suitable to the particular compound for ionization.
Posted: Tue May 10, 2005 8:53 am
by JNF
Hi,
Please check if the baseline is (too) high. It might be that the compound is hidden below the high baseline. What concentration of buffer are you using?
Before dismissing any ionisation problems related to the intrinsic properties of the compound, check if the system is not allowing your compound to "show up". I would also advise to check in a narrow scan mode perhaps you are having adduct formation or fragmentation.
Posted: Wed May 11, 2005 10:13 am
by RL
Hi,
A direct MS infusion (syringe pump) of your analyte should enable you to tune MS parameters to suit your sample. As for LC you may want to try a different buffer (formic acid for example) to enable a good signal to noise (assuming that you get a signal from the infusion of course). Good luck.