We have recently been finding that some of our LC-MS grade solvents have impurities (several brands) - notably acetonitrile and methanol. To avoid future problems, we would like to do an in-lab purification - e.g. by distillation. I have not been able to find any lab-based protocols. Is anyone able to share their protocols for lab-scale purification of high-grade solvents?
Thanks Gang. We haven't had that experience unfortunately. And by then the damage is done. There may also be a factor in the very long shipping times for dangerous goods from warehouses in the US to where we are. We've reached the point where we think it's better to be able to have some control on solvent quality in the lab.
Theoretically you can fractionally distill ACN over KMnO4 to remove any organic impurities. But it is really not easy to reach LC-MS quality. All your glassware need to be meticulously cleaned with chromic acid (con. H2SO4 + K2Cr2O7), then rinsed with high quality water and naturally air dried in a clean area. You want to set up the distillation in a separate fume hood, away from the generic organic lab and heavy traffic. No grease or O-ring allowed on any joints, including your thermometer! The distillation needs to be slow (~1 drop/s on 4L scale) so you don't have splashes or vapor carryover. Make sure to discard the first 100mL or so as a system rinse.
There is no good method to chemically purify MeOH---careful fractional distillation may be the only option.
After all these, and assume you are willing to and can deal with the toxic/poisonous nature of distilling large quantities of ACN and MeOH, there is still no guarantee your effort will pay off. Afterall, ppb level of something would be enough to throw you off.
If you want to distill LC-MS grade solvents, you are committed to a lot of efforts and investment. This is not something of a one-off impulse.
Thanks Gang - some really good tips there. We see issues with solvent variability being a long-term issue, hence unfortunately I think it's necessary to go down this route.
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