Hi,

And welcome to the wonderful world of chemistry and LC-MS!

Please be aware that preparing your mobile phases is probably the easiest step in the process of acquiring LC-MS data, so be prepared for more, and more complicated, challenges..

What flow rate will you be using in your LC method? Together with the length (time) of the overall method, including gradient, column washing and re-equilibration, and the number of blanks, controls and samples you're planning to run, you can estimate the volume of both mobile phases you'll need. Always make a bit more than you absolutely need, as it will be impossible to completely empty a glass bottle.

With regard to preparing the mobile phases, for 1 liter, prepare a stock solution of 1 M ammonium formate in water by weighing and dissolving 630.5 mg ammonium formate in 10 mL water.

Then, for mobile phase A, add 1 mL of the 1 M stock solution to 998 mL water, add 1 mL formic acid and mix. Done.

For mobile phase B, I assume you also want 0.1 % formic acid, instead of 1 mM?

Do the same: add 1 mL of the 1 M stock solution to 998 mL acetonitrile, add 1 mL of formic acid and mix and you're ready to go. Mobile phase B will also contain 0.1 % water, but that will not be a problem (I guess).

Hope this helps: good luck!

I am a little worried that you start a relatively sophisticated technique without a chemical background. Nobody to help you in your team?

Eef Dirksen gives good general directions for mobile phase prep. Use HPLC water or ultrapure water (also called "18,2  MΩ.cm") , and analytical grade reagents.

The composition of the mobile phase may change by a few % without significant problems. For example it may be simpler to add the solutions to 1 L volumetric flasks that to measure 998 mL. Similarly, weighting 630 or 631 mg ammonium formate should not make a difference. As the 0.1% water in acetonitrile.

Eef Dirksen, Thank you so much, much appreciated. This makes so much sense! 🙂

Jean-François Gal Thank you. I have high school chemistry knowledge, and I am learning as I go. Although I have a wonderful team ready to help, I want to do some background research before I start. 🙂

Dear Shahista Rojah,

Thanks for your answer. My primary recommendation is the use of analytical grade reagents and solvents.

Good luck with you experiments !

J-F

Ammonium formate has very little solubility in "100%" acetonitrile. You will need to add a little water to make it homogeneous (not sure if the 1mL used to make the stock solution would be enough).

The volume of the mobile phase to be prepared is related to the flow rate, the run time, and the number of runs in your sequence. You need enough volumes to last through your analysis (including column equilibration before analysis and washout after), but not excessively. As the mobile phase has finite stability once you put them on the machine. You don't want to keep their mobile phase for more than 3 days if you want consistent results (not critical in a research lab).

You will need MS-grade solvents and additives (i.e., your ammonium formate and formic acid). Use a dedicated set of volumatic flask, spatula, and bottles for your mobile phase preparation and don't use shared glassware.

Eef Dirksen I do believe it is 1mM formic acid, not 0.1%, so you would have a 1:1 formate/formic acid buffer pair. 0.1% FA is about 22mM, that would drown out the effect of ammonium formate completely.