Dear colleagues,
For proteomics experiments, we've purchased LC-MS grade solvents. These high purity solvents initially have already been 0.1-micron filtered (by the vendor).
To play safe, however, Would your lab filter them again via a 0.1- or 0.22-micron before their usage in LC-MS (or more specifically before the nano-LC separation)?
E.g. to remove possibly any dusts, or to remove the potentially very little amount of the eluent additive couldn't be well-dissolved (e.g. Ammonium formate or Ammonium acetate).
P.S. Would you please recommend any membrane materials that you routinely used to filter the LC-MS solvents (e.g. that are sufficient resistant to exposure to ACN or Methanol)?
Thank you very much!
Dear Kay,
I never filter the solvents because the filters often release further impurities. Rather wash thoroughfully the nano column with max 50% organic in the first day of use and monitoring the release of impurities by MS. When the column is clean, pay great attention in sample preparation and wash very well the nano-column between the runs before to return to the starting conditions for a new run.
Best regards,
Francesco
Dear Kay Wong,
I will not suggest you to filter your LC-MS solvent or HPLC grade water. Filter may be washed out with organic solvent and and can come into your solution. I genrally use new bottles for preparation and give attention to my bottles for reuse. One more thing which I take care, I always have seperate measuring cylinder for solvents and I always cover it with paraffin after use to avoid any dust. Never wash your measuring cylinder with tap water becuase it also have contamination. Wash your column with 80% ACN before you run your sample.
Dear Wong,
I completely agree with the suggestions given by Marsano and Ashutosh. LC-MS grade solvents doesn't require any further filtration. But as mentioned by you, if you are preparing ammonium formate or acetate based solvents containing ACN, FA/TFA etc., probably you may consider filtering with PTFE (Polytetra fluroroethylene) filters. I have used them and they work absolutely fine. These filters are robust and are compatible with organic solvents, they dont leach out ...
All the best for your efforts
Saravanan K
Dear Wong
As you can see the general consensus is to avoid further filtration of purchased MS grade solvents. The reason is that additional filtering introduces more contaminants than you will remove as there are no filtration systems or membranes that are contamination free.
Addition of MS grade formate will not require further filtration either as both are solutions.
Which protocol do you want to use that requires addition of ammonium formate? Proteomics peptide separations on nanoLC systems are generally run under positive ion mode which requires acid (formate addition) conditions.
If you do require low concentrations of ammonium formate or ammonium acetate it is best to buy these from the vendor already made up in relatively small volumes (100 ml) and use the containers in which they are delivered directly as the mobile phase reservoirs as transfer to other containers also holds a contamination risk.
Cleaning the column before use and running a blank before your samples can eliminate some unidentifiable peaks in your chromatograms
All the best
Duncan
Dear Professor Cromarty,
Thank you very much for your very helpful advices.
Yes, our lab would require low concentrations of ammonium formate or ammonium acetate.
Nevertheless, for the commercially available formats - we couldn't find any that is readily available as LC-MS grade ammonium formate or ammonium acetate solution.
They seem to only available in other formats:
LC-MS grade crystalline, non-LC-MS grade solution, or pre-blended in solvents (e.g. 0.1% ammonium acetate in ACN or water).
Would you please further advice? Appreciated.
I agree with the consensus... always problems with keeping filters clean enough and each operation is seriously infringing concerning lab contamination. I have had a hundred times problems with stuff that was flying around in the lab, but very rarely with solvents purchase with a reasonable quality from a serious vendour.
I do not run nano HPLC, but I guess we all just use the formates we get as is. usually only in your eluent with a few %
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