Chromatography Forum

I recently received a Waters 2795 from donation, which passed PM just prior to my receiving it. I also have a brand new column that I tested on another system with the test mix and know that the column is in perfect condition. Once I set this 2795 up, I ran the test mix on this new column and I am seeing a significant amount of peak fronting. Since the method is tried and true, as is the column, I am uncertain what could be causing peak fronting. One further note is that my diluent is the same as my mobile phase. Everything I know about peak fronting usually points to one of these as the probable factor influencing the poor peak shape.

The only other thing I can think of is that maybe my tubing isn't in connected properly and is causing a void between the tubing and the inlet or outlet of the column. I'm almost 100% certain this is a system issue of some sort, I just can't think of anything else I can pinpoint to be the problem. I was thinking I would re-plumb the system tomorrow, unless anyone else could give me any other bright ideas that might be reasonable options. This is my first time using a 2795, so I didn't know if there was something inherent to this type of LC that I needed to be aware of when trying to troubleshoot this issue. Any other insight would be greatly appreciated!

Thanks!

If your check sample has more than one peak and they all tail (or front) similarly, that's evidence of some kind of "flow anomaly". The exact effect is hard to generalize because "the devil is in the details". I think you're on the right track looking for problems in tubing, connections, etc.

If memory serves me this model has separate strong and weak needle wash solvents. If this is the case, the weak needle wash solvent should be weaker than your mobile phase. I've used 5 v/v% methanol in H2O for the weak needle wash solvent without problems.

i agree with carls
this is the "improved" 2 solvent wash solution model
check the wash solvents as well and the settings you have in empower for the wash
the 2 main things that can occur when not using the good solvents in those modules is:
peak shape distortion- fronting if using too high organics%
really bad RSD as well

one line must have a "weak" wash solution, and it must be very close to the mobile phase you use
the "strong" solvent is there to allow you to clean very well the sampler needle and prevent the carry over that is one of the major flaw of the 2695 modules. you need to wash the strong solvent with enough weak solvent in the end to prevent the possible problems above.
if you have no idea on how to use it, best put a wash solution that is close to the mobile phase in both bottles, as do 90% of the users for the 2795 and the UHPLC as well

Just wanted to say Thank You! I had no idea about the intricacies of the new wash functionality of this system. Once I got that under control, I had beautiful peak shape. Thanks for the input!