Chromatography Forum

At low wavelength, the background absorbance is dominated by the TFA concentration. The TFA concentration varies to some degree with the TFA feed. If you have a mixer, the feed is much smoother. Secondly, the TFA is adsorbed on the packing, which then in turn amplifies the differences in mobile phase composition.

I am not aware of any demonstration that ruby check valves play a role in this.

In my experience the baseline fluctuations due to such small changes in flow rate are much less than the "ripples" shown in the above chroms, as a matter of fact one wouldn´t have seen them on the scale chosen for these. Besides, the results reported by sdegrace clearly show that bad mixing of TFA was the culprit (as predicted and theorized by several participants here).

HW:

Is it possible that the mixer can also compensate the fluctuation caused by check valves? I am not sure how big the fluctuation is, but it is not necessary small (the small check valve can shut down the entire flow though).

In our lab, we tried on three different Alliance 2695 systems using the same mobile phases containing 0.05% TFA. Each time after we replace the ruby ball check valve with ceramic check valve, the baseline dramatically improved. If we change back, the baseline became noisy again. We don't have a clearcut explanation on it, but the results definitely pointed to the failure of ruby check valve under these conditions.

Hopefully anyone can come up with reasonable explanations. That will be a big help to us too.

Regards,

Or it could simply be old ruby check valves versus new ceramic check valves...

Bottom line: if it worked for you, be happy...

Uwe:

Both new and old ruby ball check valves behave similarily.

I agree with you, as long as it works......

Regards,