Buffers and Degassing

[ravenwork]

Greetings,

I are performing gradient RP HPLC for environmental analysis. I usually pump pure solvents with low pressure mixing, and He sparging.

I am seeing some unacceptable retention time shifts with a new method. The shifts appear to be sample matrix related. I suspect a pH effect since we are running unbuffered with pure solvents.

I would like to try buffering the water. Phosphate is not a good choice since the samples contain calcium chloride. I want to try a formate buffer, but I am concerned about its volatility. Since we generally use pure solvents, we just sparge continuously. Am I right in thinking that continuous sparging of a formate buffer may change its pH over time due to evaporation of the formic acid? Can I sparge for 30 minutes and then maintain a He blanket in the vessel?

ravenwork

[tom jupille]

Probably 5 minutes of sparging will suffice.

[Kostas Petritis]

I used in the past a similar mobile phase with a Dionex (LC-Packings) nano-pump and I didn't observe any problems of formic acid evaporation. Once you prepare the mobile phase you start by sparging relatively intensively, then after 5 minutes you decrease the He flow rate to a minimum...