cleaning h3po4 contamination in lc-ms

[csmith731]

I had to run a sample using 0.04% h3po4 as one of the mobile phases. I ran a cleaning mix of 1:1:1:1 MeOH, H2O, IPA, and ACN with 1% formic acid overnight. It still is not cleaned. How can I remove the phosphoric acid

[tkubowicz]

Hello

Have you flushed all flow paths? Normally samplers have bypass positions so make sure it is flushed. Also flushed LC for all possible valve/s positions.
If problem still exists try to narrow it down:
-connect only pump to detector and see if you still have contamination. Then connect modules (LC components) one by one to see which part is problematic one.

Regards

Tomasz Kubowicz

[carlo.annaratone]

You might want to clean the MS source and cones/capillaries as well. Phosphoric acid is non-volatile, and may form deposits there

[mckrause]

First, it's a really, really bad idea to run any non-volatile salt through a MS, as you clearly found out.

H3PO4 is nasty - it likes metal surfaces a lot. Your going to have to break your system down and clean everything up to the quad. I would use a very dilute isopropanol solution or even just DI water, and then rinse well with solvents and bake.

You're also going to have to clean your entire flow path - pump heads, autosampler, MS divert valve, etc.

You might be able to get it to clean up running straight DI water with no column. Set up a really long run (the longest your software will allow you to use) and let it pump. However, I'm betting you're going to have to break it all down and really clean.

Same problem with TFA, by the way. Avoid it in your MS like the plague unless you really, really don't ever want to run negative ion.