As recently shown DMSO enhances electrospray response (see Hahne et al, Nat Methods. 2013: DMSO enhances electrospray response, boosting sensitivity of proteomic experiments. http://www.nature.com/nmeth/journal/v10/n10/full/nmeth.2610.html). We also have seen higher identification rates in complex samples using 5% DMSO in the LC-buffer for our Orbitrap Velos Pro: 30% more PSMs and 20% more peptides and protein groups.
What we like to know is your experience with DMSO effects on the hardware side (MS and/or LC). It is pretty clear that there is an enhancement to IDs but before going to high-throughput with DMSO in the running buffer we like to ensure that there is no negative impact on the hardware. Some engineers recommend avoiding DMSO due to its effect on the ion optics pathway of the MS.
Bernhard Kuster gave a talk at the recent ASMS meeting and presented his findings. In summary it was that he does need to clean his instruments more frequently, but they are persisting with DMSO as the benefits are tangible. Don't quote me, but I think the time between cleaning was halved, so every 6-7 weeks instead of every 12-14 weeks.
He also included feedback from others that had tried DMSO. Most did find an improvement, some found little difference, and some even saw a decrease in identifications. Clearly you are seeing an improvement.
We haven't started using it yet as I am concerned about the cleaning aspect. I guess you need to decide for yourself if the improvement is worth the more frequent cleaning. Kuster certainly came to the conclusion that it is worth it.
In our hands, the advantages of using DMSO are limited. Some signals are really improved, but the ion optics gets dirty much more frequently.
Should be much better idea to use specific new ion sources that orthogonally use other "helper" compounds such as acetonitrile for ionisation improvment.
Thanks so far for your feedback.
In summary, DMSO seems to require slightly more frequent instrument cleaning. If I got the statement correct, Berhard Küster mentioned a turnover of ~3-6 weeks in his ASMS talk.
Did anybody checked for some other solvents besides DMSO like DMF (Dimethyl Formamide) for enahancement of electrospray response?
DMF has a lower boiling point (153.0°C) and surface tension (36.76 dyn/cm at 20°C) than DMSO (boiling point: 189 °C, surface tension: 43.54 dyn/cm at 20°C), but a boiling point that is still higher than water. If their theory about surface tension is correct then this might work better (and hopefully with less dirt at the ion optics!)
A word of caution! We tried the published method (5% DMSO in HPLC solvents) and had similar improvements in peptide identification metrics (not quite as big of an improvement but significant). On one instrument (Eksigent nano LC - Obritrap Velos) we had unacceptable signal loss in approximately 3 days and our instrument required cleaning. Another instrument (Agilent 1200 nano LC - LTQ-FT plus) was fine for 1 month before cleaning was required. We had used a new bottle of DMSO that was the same one described in the methods paper (same supplier and grade). Before switching over to DMSO in our solvents we would clean the LTQ-FT once a year and the Orbitrap Velos about once every six months. Maybe this is a worst case scenario and the DMSO "extracted" contaminants that had built up for months before switching over. At the time we weren’t sure it was the DMSO and we ran after these cleanings with DMSO and had to take the instruments down again. Our Thermo service engineer reprimanded us as he knew running DMSO was not a good idea.. my advice is to talk to your service engineer before making the switch to DMSO in your solvents. If you decide to run DMSO, think about precondition your LC system off-line of the MS. Good luck!
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