Random dip(s) in baseline

[bashleigh]

Hey everyone -

We've seen this a number of times in our lab and I'm trying to figure out what it is so we can prevent it from happening in the future.

We're running on Agilent 1200s and have seen similar dips in baselines in several methods, but the one I'm posting pictures of is a gradient method with 0.1% TFA in water and 0.1% TFA in acetonitrile as mobile phases.

Does anyone know what causes these random dips and spikes in the baseline?


Black = Standard injection (with dips)
Brown = Blank
Green = Standard injection (normal)


Black = Standard injection (with dips)
Blue = Blank (normal)
Pink = Sample injection right after the Standard with dips.

Any help would be greatly appreciated! Thanks!
-brooke-

[nschwartz]

More questions need to be answered to find a solution for this.

First off, does this ever happen with your blanks? Do your blanks contain the same solvents as your standards? Is there a difference in the materials used for your vials and caps or transfer pipets used for standards?

[bashleigh]

It happens completely randomly. Blanks, standards, samples, you name it....at any time in the gradient. It it doesn't happen a lot; but, when it does, it's quite a pain.

Blanks and standards contain the same solvents (which in the case of the pictures posted, is the same as initial conditions of the HPLC run).

Transfer pipettes used were the standard polyethylene ones, and the HPLC vial caps used had a PTFE septum; vials were amber glass.

It tends to happen more in methods we run that have longer run times (i.e. 50-60 minutes).

It could be something as simple as a bubble being pushed through the system, I'm sure - but was wondering if anyone else has experienced something similar and actually attributed it to something specific.

thanks!

[tom jupille]

If you are using the two-pump (high pressure mixing) version of the 1200, you might be looking at one of the pumps choking on an air bubble which the gradually redissolves.