How often do you make mobile phase?

[sjmarin]

I am taking an informal survey on how often people prepare fresh mobile phase. Most of our mobile phases are some combination of methanol/formic acid and aqueous ammonium formate/formic acid. The lab makes fresh mobile phase every 3 days, but I think these should be stable for at least a week at room temp. Does anyone make big batches and store it in the fridge? We do LC-MS/MS, so we don't want to gunk things up. Thanks.

[weeker2001]

i am in a government lab ,the main work is analysis medicine ,and everyday ,the sample is different,so i need to prepare the mobile phase each time .i cannot use the mobile phase several days ago ,then i guess the buffer will produce germs or other microorganism.

[tom jupille]

Aqueous buffers *will* grow bugs. If you use the same kinds of buffers frequently, you will do selective breeding for bugs that can metabolize those buffers efficiently, and your buffers will have to be prepared fresh daily (ask me how I learned this! ). In my experience, 5 - 10 % MeOH is sufficient to inhibit bug growth.

My take on things is that it's better to be conservative re mobile phase life.

[lmh]

For LC-MS applications you also need to consider sodium leaching into solutions from glass bottles. I have some analytes where I see a hydrogen adduct as base peak on day 1, and a sodium adduct 24 hours later (water taken initially from typical lab RO machine). This may not be terribly important, depending on application.

I used to make fresh aqueous buffers every day; when busy, I'm now prepared to use yesterday's buffer, because of time-pressure. That's as far as I trust things.