Increase in absorbance over the course of a gradient analysis injection run.


I am looking for advice on how to fix what I am observing in my HPLC Agilent 1220 Infinity II. Thank you in advance for any insight.

When my HPLC is on the absorbance at 230nm baseline is flat and does not move from 0. However, when I run an injection (either with volume of blank methanol or with an injection volume of 0) the absorbance will shift upwards as the gradient method increases in the % of methanol coming from bottle B.

As seen in the picture there is an upward trend over the course of the run.

Bottle A : 0.1 % (v/v) Formic acid in water aqueous phase & Bottle B 0.05 % (v/v) Formic acid in Methanol  organic phase.

Time (min) % B

0                 60

1.0              60

7.0              77

8.2              95

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