Baseline drift in gradient system

[vanjas]

Hi!!
My question is about linear baseline drift in gradient system.
I employ the method as an linear gradient mode using Phosphate buffer and aceonitrile.
Is it normal phenomenum on that kinds of drift? And is it applicable on the calculationeven if the baseline give some decrement on impurity peaks?
Any help would be really appriciated for me !!
Thanks for your attention on this matter in advance..

[Sallybeetle]

I found this in the Chromatography Forum archive.

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By Tom Mizukami on Tuesday, December 11, 2001 - 05:21 pm:

The UV cutoff for acetonitrile is 190nm, that is it has a UV absorbance of 1AU in a 10mm cell at 190nm.

The sharp drift in baseline is either due to the absorbance of acetonitrile at 240, which is negligible, or refractive index change of your mobile phase. If the base line is curved and peaks at about 50% ACN then it is due to refractive index. If it is linear and it is a maximum at 85% then it is due to absorbance.

You determine LOD just as you would if the baseline was not sloping. The sloping baseline just makes it more difficult to find adequate integration parameters.

If your drift is due to refractive index your only real option is to try a different detector. Make sure your cell is aligned correctly etc.

However, if the slope is due to absorbance, you can match the absorbance of the A and B components. Assuming that you are using water for the aqueous fraction and that your baseline is sloping up you can try adding sodium azide (or urea, nitrite, nitrate, etc) 20-200ppm to the 35% acn solution and see if you can find a concentration that will make the drift disappear.

Good Luck

[Rafael Chust]

Dear Vanjas:

Besides the UV drift - which is possible - as you are increasing your solvent strenght it may also be related to organic impurities catch at the colum in previous injections.

[syx]

Besides the UV drift - which is possible - as you are increasing your solvent strenght it may also be related to organic impurities catch at the colum in previous injections.

Rafa, do you mean late elution of impurities from previous injection that appear as broadening peaks? Impurities from mobile phase or sample solution will be eluted as ghost peaks when the solvent strength increased in gradient run.

[Rafael Chust]

Dear Syx:

In fact, books and experience refers ghost peaks - that I personally define as nice peaks coming from nowhere!

But baseline drift, from my experience, can be caused by impurities coming out of the column - usually larger organic molecules that stays trapped in the column and comes out when you increase solvent strenght.

Other situation that might also appears as baseline drift is the removal of C18 groups coming out from stationary phase - even in normal conditions - and this becomes more evident when the column is getting older. Of course, you must check other "signs" for this "alien" phenomenons.