Chromatography Forum

Hello all,

I am attempting to develop a method for an acidic compound.

I would like to know what is the optimal concentration to inject or infuse on my system.

I have a Agilent 6410 QQQ LC/MS/MS,

What should be the initial concentration starting range to see a clear view of the molecular ion?

My front end LC is an Agilent 1200 series.

Would I do a full scan MS2 Scan injecting 5, 10, 15uL ? What sort of concentrations?

So far I have injected a 2,000ng/mL standard made up in mobile phase, 5uL injection, but failed to see the molecular ion?

Thanks so much.

we normally inject 5 to 10 uL of a 10 ng/uL solution (5x - 10x of yours). same concentration is used for infusion at a rate of 5-20 uL/min.

that's pretty high concentration to identify your molecular ion (which of course may not be visible if you get an adduct with formate in negative ESI or with sodium in positive ESI, for example)

You should be able to see a molecular ion at that concentration in full scan Q1 or Q3 mode--i.e., no Q2 fragmentation. Since it is an acidic compound, you might want to look in negative ion mode. I recommend scanning a large enough range around the molecular ion to see water losses, Na adducts, etc. Also, check the literature to see what ions others have used for your compound or closely related compounds.