Chromatography Forum

Hello forum,
i need your assistance!
I have to determine a analyte with the following LC/MS method:
mob.phase= water:acetonitril:trifluoroacetic acid:1 M NaOH=990:10:1,5:7,5
analyte will be determined as the M+Na
I get strong signals in my background: 159 amu / 295 (159+136) / 431 (295+136)
which are suppressing the ionsisation of my analyte. Further exploration showed, that the backgroundsignals disappeare, when i omit the 1M NaOH. When i use 0,1M NaOH instead of 1 M NaOH (0,75 mM Na instead of 7,5mM Na) i get much better ionisation of my analyte!
When i use formic acid instead of trifluoroacetic acid i get the following background:
159 / 227 (159+68) / 295 (227+68) / 363 (295+68) / 431 (363+68) .. and so on.
What can this be? How can i get rid of this Impurity?
Best regards
pillin

a lot of people used mixtures of acids to calibrate. This is because you get clusters of these charged species.

Thus for formic acid and NaOH will get Na(NaO2CH)n where n=0,1,... in the positive ion mode for

m/z 23, 91, 159, 227,...

Need to avoid significant concentrations of salts containing inorganics cations, will just "steal" all your ion current and suppress your signal.

Almost always will see some M+Na signal for an analyte at higher skimmer or cone voltages even when no sodium deliberatley added.

I would try with less acid and NaOh in your phase first.
0.01% TFA is more commonly use for MS.
It will be intereting to see what is the pH of your phase and which one would be better for your compound.
what is the RT of your compound?

pablo.