Baseline drift
Chromatography Forum: LC Message Board: Baseline drift
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By Anonymous on Tuesday, July 6, 2004 - 12:37 pm:

Hello Im from argentina and I started development a platform for impurities and amines compound with these movile phases.
Methanol /water 30:70 and 80:20 both with 0.1% de TFa I have problem with the baseline drift and a peak when started a gradient before 6 minutes hold.
Sorry with my english

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By Anonymous on Tuesday, July 6, 2004 - 01:51 pm:

that's normal when you run a gradient, because the solvent change over time, if you use a PDA-detector you can substract the backgound, by using the ref.wavelenght.

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By diego cobice on Wednesday, July 7, 2004 - 02:46 pm:

Yes, but may wavelength is 220 nm,and when I started a gradient profile with a hold of 5-dwell time and at these moment a peak appears at time 6.5 minutes and then the gradient run.a question? TFA is the only compound that I put in my movile phase to put it them at 2.2 UpH, because formic , acid, phosphoric acid, and buffer phosphate my baseline is not stable.
Thanks for your help!!!

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By Chris Pohl on Saturday, July 10, 2004 - 03:09 pm:

Diego,

TFA absorbs at low wavelengths so you're asking for trouble trying to use it at 220 nm. On the other hand, if you had a problem with phosphoric acid, you need to try a higher purity source. Phosphoric acid is UV transparent at 220 if free of impurities. I suggest you buy the HPLC grade available from Fluka in ampules (or another source of HPLC grade phosphoric acid).

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By dcobice on Wednesday, July 28, 2004 - 07:07 am:

thanks, but now I run a platform like that...
70:30 water:methanol(a) and 80:20 methanol: water,
a linear gradient using an alliance waters HPLC.
My baseline is like a sinusoidal beseline
I dont know what happpend?????

Sorry with my english!

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By Chris Pohl on Friday, July 30, 2004 - 01:55 am:

If you see a sinusoidal baseline when doing a TFA gradient, your problem is mixing. Oscillating levels of methanol in your mobile phase due to incomplete mixing cause fluctuations in the amount of TFA in the mobile phase (since the amount of TFA adsorbed on the stationary phase is dependent on the amount of methanol in the mobile phase). You can prove this by replacing the column with a piece of small ID tubing sufficient to add at least 500psi in order to the maintain some backpressure on the checkvalves. If the oscillations go away when you run a gradient with this setup, you know its a mixing problem. To fix the problem, add a larger mixer. Several supply houses (such as Upchurch) have HPLC mixers for such problems.

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By dcobice on Tuesday, August 10, 2004 - 08:29 am:

thanks a lot for your request!!! other thing...
my head pressure is about 3000 psi in a ODS-3, 4.0Id and 3.0 um using at the begining 70/30 water/methanol.. it can affect the column life?
or affect any chromatographic suitability parameters???

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By Uwe Neue on Sunday, August 15, 2004 - 07:17 pm:

3000 psi is not a problem, if it remains constant and is not constantly climbing. What is your column length?