Chromatography Forum

I am using a Agilent 1260 Infinity II FLD (part number G7121B) with baseline set to free and seeing an LU response of 0.6 LU which has steadily increased from 0.3 LU over the past year. I am running a gradient method which starts at 80:20 ACN:25mM Ammonium Formate buffer (pH 4.0). The method is used for the detection of impurities and I am concerned that if the baseline continues to rise it will mask the detection of impurities. I have already tried cleaning the flow cell with a number of solutions (purified water, dilute nitric acid, a combination of alcohols with 0.2% O-Phosphoric Acid) and baseline has remained around 0.6 LU.

Does anyone know a better way to clean the flow cell to get a lower LU response? Is my concern about the masking of impurity detection unfounded?

Thanks in advance,
G

Look at the signal-to-noise ratio (average of several calculations) for one of your analytes. Compare the value you have now and the value you had a year ago. The rise of the baseline level (and noise) and the increase in the baseline slope upon gradient elution is more likeky caused by the dirty column than by the dirty FLD cell.

Look at the signal-to-noise ratio (average of several calculations) for one of your analytes. Compare the value you have now and the value you had a year ago. The rise of the baseline level (and noise) and the increase in the baseline slope upon gradient elution is more likeky caused by the dirty column than by the dirty FLD cell.

Thanks for your reply. My suspicion that the flow cell was dirty was due to use of the same column on a different FLD showing a markedly different baseline starting point (around 0.3 LU).

Does that detector come with different flow cell options?
I'm hearing that longer cells are problem-prone... but that may just be the cells for UV/Vis.

Does that detector come with different flow cell options?
I'm hearing that longer cells are problem-prone... but that may just be the cells for UV/Vis.

Indeed there is a 4uL and an 8uL flow cell. I am using the 8uL. Might be something I could look into. Thanks!

It's actually more about the path length... 6 good, 10 not so reliable.