Baseline drift upward

[hplcnewuser1]

Hi, quick question about baseline. It was drifting upward due to gradient 20-95%B. (A is tfa water B is 90% tfa ACN). When I prepared fresh MP B baseline drift increased from 70mAU up to 170mAU.
MP was made same way as the previous one using volumetric pipete.
What could cause this upward drift to increase?
Thanks

[HPLC chemist]

Any drift could be due to the refractive index or absorbance differential between the mobile phases. It is not significant if you are using the autozero function before every injection.

[Peter Apps]

Any drift could be due to the refractive index or absorbance differential between the mobile phases. It is not significant if you are using the autozero function before every injection.

The question was why the drift increased with the new batch of mobile phase, not why drift happens.

If the column is properly re-equilibrated between runs then autozeroing at the start of a run should make little or no difference, and if the column is not re-equilibrated using autozero to mask the baseline shift will mask a potential cause of retention shifts and peak distortions.

hplcnewuser1; did you use the same source of all the components in mobile phase B for both batches ?

do you leave mobile phase flowing when the HPLC is on standby - and was the standby time longer for the new batch of mobile phase ?

Is the drift consistent from run to run ?

Peter

[hplcnewuser1]

tfa ACN and tfa water same lot. I equlibrate starting analytical conditions 80%"A"(100%0.1%tfa water) 20%"B"(90% of 0.1%tfa ACN) for about 15min untill baseline is flatthen also zero it to make sure it is perfectly flat. not usre hwat you mean by standby but there is always this mixture 80/20 running after each run to reequlibrate for the next run. I did stop the flow while making fresh MP.

baseline drift is smaller with each consequtive injection, so the peak looks better by the end of day then at beginning. It baseline ramps up as B is increased and when B is 95% it holds steady arund 175mAU which sucks for the peak. It does decrease to about 75mAU after 10 runs
Sample is in tfa water not starting 20% ACN, because it would precipitate.
thank you

[Peter Apps]

The drift getting smaller with consecutive runs sounds as if something is getting deposited on the column before you start a batch of samples - this would point to a problem with the purity of the components of mobile phase A.

Peter